Digital SPWM (Sinusoidal Pulse Width Modulation) method

Abstract

The invention discloses a digital SPWM (Sinusoidal Pulse Width Modulation) method, which comprises the following steps of: 1) sampling a modulation wave, acquiring a sampling value x as input data, and solving an estimated value at a peak value which is closest in advance by utilizing a discretized advanced transfer function; sampling the modulated wave to obtain sampling input as input data, and solving an estimated value at a peak value closest to lag by using a discretized lag transfer function; (2) solving an intersection point of a modulated wave and a carrier wave by utilizing a pre-estimated value at the nearest peak value before and after the sampling value and the current sampling value and by adopting a triangle replacement method and utilizing the similarity relation of triangles; and 3) solving the duty ratio in the carrier wave period by using the carrier wave period and the intersection point relationship. Compared with a natural sampling method, the modulation method is small in calculated amount; compared with a symmetry method, the precision is high.

Description

Technical Field

[0001] The invention relates to a digital SPWM modulation method, belonging to the technical field of power electronics and control. Background Art

[0002] When power electronic products are working, pulses are needed to control the on and off of IGBT. SPWM pulse width modulation technology is often used in pulse width modulation. There are usually two methods: natural sampling and symmetrical sampling. The high precision of SPWM (sinusoidal pulse width modulation) can make the output of the inverter closer to the sine wave. The sine wave is used as the modulation wave and the isosceles triangle wave is used as the carrier for comparison. The on and off of the switch device is controlled at the natural intersection of the two waveforms. This is the natural sampling method. Its advantage is that the obtained SPWM waveform is closest to the sine wave, but because the intersection of the triangle wave and the sine wave is arbitrary, the pulse center is not equidistant within a cycle, so the pulse width expression is a transcendental equation, which is cumbersome to calculate and difficult to control in real time. Therefore, symmetrical sampling is often used in engineering. This method generally uses a triangle wave as a carrier. The principle is to use a triangle wave to sample the sine wave to obtain a step wave, and then control the on and off of the switch device at the intersection of the step wave and the triangle wave, thereby realizing SPWM modulation. However, the symmetrical sampling method cannot obtain the correct intersection of the modulation wave and the carrier, so the error is large. Summary of the invention

[0003] The technical problem to be solved by the present invention is that power electronic products require pulses to control the on and off of IGBTs when working, and natural sampling and symmetrical sampling are used for pulse width modulation. When natural sampling is used, the calculation amount for solving transcendental equations is large, and when symmetrical sampling is used, the error is large.

[0004] In order to solve the above technical problems, the present invention provides a digital SPWM modulation method, comprising:

[0005] 1) Sample the modulated wave, obtain the sampled value x as input data, and use the discretized lead transfer function tf1 to obtain the estimated value at the nearest lead peak;

[0006] Sample the modulated wave, obtain the sampled input x as input data, and use the discretized lag transfer function tf2 to obtain the estimated value at the nearest lag peak;

[0007] 2) Using the estimated value of the nearest peak before and after the sampling value and the current sampling value, the triangle replacement method is used to solve the intersection point of the modulated wave and the carrier wave by using the similarity relationship of the triangle;

[0008] 3) Using the relationship between the carrier period and the intersection point, calculate the duty cycle within the carrier period.

[0009] In the aforementioned digital SPWM modulation method, in step 1), the lead transfer function is a SOGI-QSG type function, and the input data is filtered using the lead transfer function, and at the same time, the lead angle is obtained according to the different carrier frequencies. The estimated value of x1;

[0010] The complex frequency domain expression of the lead transfer function is:

[0011]

[0012] in, represents the lead transfer function, k represents the closed-loop coefficient, represents the resonant frequency of SOGI-QSG, represents the complex variable of the Laplace transform.

[0013] In the aforementioned digital SPWM modulation method, in step 1), the execution process of the lead transfer function is:

[0014] The input signal x is at the phase-locked angle Perform abc-dq phase coordinate transformation under;

[0015] After the abc-dq phase coordinate transformation, the signal is Perform dq-bac phase coordinate transformation;

[0016] The time domain calculation formula of the lead transfer function is:

[0017] .

[0018] In the aforementioned digital SPWM modulation method, in step 1), the hysteresis transfer function is a SOGI-QSG type function, the hysteresis transfer function filters the input data, and at the same time obtains the hysteresis arbitrary angle according to the different carrier frequencies. The estimated value x2, the complex frequency domain expression of the lag transfer function is:

[0019]

[0020] in, represents the hysteresis transfer function, k represents the closed-loop coefficient, represents the resonant frequency of SOGI-QSG, and s represents the complex variable of Laplace transform.

[0021] In the aforementioned digital SPWM modulation method, the execution process of the hysteresis transfer function is:

[0022] The input signal x is at the phase-locked angle Perform abc-dq phase coordinate transformation under;

[0023] After the abc-dq phase coordinate transformation, the signal is Perform dq-bac phase coordinate transformation;

[0024] The time domain calculation formula of the lag transfer function is:

[0025]

[0026] After estimating the parameters of the leading transfer function and the lagging transfer function at any angle, the estimated parameters are bilinearly transformed to complete the parameter discretization process for use in the digital controller.

[0027] In the aforementioned digital SPWM modulation method, in step 2), in the triangle replacement method, the arc between the intersection of the modulation wave and the carrier is replaced by a straight line BCD at a high carrier frequency, thereby constructing triangles ABC and DCF, point A is the peak value of the positive half cycle of the carrier, point B is the intersection point of the modulation wave when a perpendicular line is drawn from point A to the time axis, point C is the intersection point of the modulation wave and the carrier, point D is the intersection point of the modulation wave and the time axis, point E is the peak value of the negative half cycle of the carrier, point F is the intersection point of the time axis when a perpendicular line is drawn from point C to the time axis, and point G is the intersection point formed by a line drawn along point B parallel to the time axis and AE;

[0028] The on-length of PWM is DF, and the off-length of PWM is BG. At high carrier frequency, the arc BCD is replaced by the straight line BCD. According to the relationship of the triangle, the effective high and low pulse time of PMW is obtained, where the height coordinate of point B is x1, which is the previous input, and the height coordinate of point D is x, which is the current sampling input;

[0029] There is a triangle ,and ,get:

[0030] (2)

[0031] (3)

[0032] According to the relationship between equations (2) and (3), equation (4) can be obtained:

[0033] (4).

[0034] In the aforementioned digital SPWM modulation method, in step 3), AB=1–x1, ED=1+x, BG+DF= / 2, is the carrier period, then the high level time t in the corresponding half cycle is obtained DF , the calculation result is shown in formula (5):

[0035] (5)

[0036] The modulated wave intersects with the carrier at point H, and the height coordinate of point H is x2. Similarly, the high level time on the right side of the sampling is calculated:

[0037] (6)

[0038] The high level time of the whole cycle is:

[0039] (7)

[0040] The low level duration within the cycle is obtained:

[0041] (8)

[0042] The PWM waves are maintained in sequence within a PWM cycle Ts. L1 The duration of low level, t H The duration of high level and t L2 The low level of the duration, where t L1 ,t H ,t L2 They are:

[0043]

[0044]

[0045]

[0046] Find t L1 , t H , t L2 The actual value of is the high and low level time within the carrier cycle, where x is the sampling input of the current modulation wave, and x1 is the lead after the lead transfer function calculation. The lead estimate of the angle, x2 is the lag after the lead transfer function is calculated The estimated hysteresis of the angle, t L1 is the first low level time, t H is the high level time, t L2 This is the second low level time.

[0047] In the aforementioned digital SPWM modulation method, in step 3), according to the obtained high level time and low level time, a digital cycle register is used to judge the relationship between the value of the cycle register and the high and low level time by increasing the value of the register, and the corresponding high and low pulses are generated to complete the modulation.

[0048] In the aforementioned digital SPWM modulation method, in step 3), when the per-unit value t of the cycle counter is less than t L1The output is low level when t is greater than t L1 and less than t L1 + t H The output is high level, t is greater than t L1 + t H And it is less than Ts, which is a low level, completing the modulation.

[0049] A computer device / equipment / system comprises a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the above method.

[0050] A computer-readable storage medium stores a computer program / instruction, which implements the steps of the above method when executed by a processor.

[0051] Beneficial effects achieved by the present invention: A digital SPWM modulation method proposed in the present invention utilizes lead and lag transfer functions and approximate trigonometric relationships to solve for estimated values ​​of any lead and lag angles, and further solve for the approximate intersection of the modulation wave and the carrier, thereby obtaining the high and low level times of the pulse width. Compared with the symmetric method, the accuracy of pulse width modulation is improved, and the output waveform can be made closer to a sine wave.

[0052] A digital SPWM modulation method of the present invention, wherein the SOGI-QSG type cycle extension transfer function can filter the modulation wave and estimate the leading and lagging parameters at any angle. When used, the transfer function can adjust the parameters according to different carrier frequencies, has strong operational flexibility, can reduce the amount of engineering calculations, and avoids the problem of solving transcendental equations. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 A digital SPWM modulation method implementation flow chart in Embodiment 1 of the present invention;

[0054] Figure 2 A diagram showing the relationship between a carrier wave and a modulation wave in a digital SPWM modulation method in Embodiment 1 of the present invention;

[0055] Figure 3 This is a schematic diagram of equivalent calculation of a digital SPWM modulation method in Embodiment 1 of the present invention;

[0056] Figure 4 An input-output diagram of a leading transfer function of a digital SPWM modulation method in Embodiment 1 of the present invention;

[0057] Figure 5 An input-output diagram of a hysteresis transfer function of a digital SPWM modulation method in Embodiment 1 of the present invention;

[0058] Figure 6This is a pulse waveform diagram generated by modulation using a digital SPWM modulation method in Example 1 of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0060] Example 1

[0061] This embodiment provides a digital SPWM modulation method, including:

[0062] 1) Sample the modulated wave, obtain the sampled value x as input data, and use the discretized lead transfer function tf1 to obtain the estimated value at the nearest lead peak;

[0063] Sample the modulated wave, obtain the sampled input x as input data, and use the discretized lag transfer function tf2 to obtain the estimated value at the nearest lag peak;

[0064] The advance transfer function is a SOGI-QSG type function, which uses the carrier period to determine the advance data lag Graphical representation of an angle.

[0065] In step 1), the lead transfer function is a SOGI-QSG type function. The SOGI-QSG (second-order generalized integrator quadrature signal generator, SOGI-QSG) algorithm is a phase-locked loop algorithm based on a three-phase signal. The lead transfer function is used to filter the input data, and at the same time, the lead angle is obtained according to the different carrier frequencies. The estimated value of Figure 4 As shown, find out the advance estimated value x1;

[0066] The complex frequency domain expression of the lead transfer function is:

[0067]

[0068] in, represents the lead transfer function, k represents the closed-loop coefficient, represents the resonant frequency of SOGI-QSG, represents the complex variable of the Laplace transform.

[0069] The execution process of the lead transfer function is:

[0070] The input signal x is at the phase-locked angle Perform abc-dq phase coordinate transformation under;

[0071] After the abc-dq phase coordinate transformation, the signal is Perform dq-bac phase coordinate transformation.

[0072] The time domain calculation formula of the lead transfer function is:

[0073]

[0074] The hysteresis transfer function is a SOGI-QSG type function. The hysteresis transfer function can filter the input data and obtain any hysteresis angle according to the different carrier frequencies. The estimated value of Figure 5 As shown, the lag estimation value x2 is obtained, and the complex frequency domain expression of the lag transfer function is:

[0075]

[0076] in, represents the hysteresis transfer function, k represents the closed-loop coefficient, represents the resonant frequency of SOGI-QSG, and s represents the complex variable of Laplace transform.

[0077] The execution process of the hysteresis transfer function is:

[0078] The input signal x is at the phase-locked angle Perform abc-dq phase coordinate transformation under;

[0079] After the abc-dq phase coordinate transformation, the signal is Perform dq-bac phase coordinate transformation.

[0080] The time domain calculation formula of the lag transfer function is:

[0081]

[0082] After estimating the parameters of the lead transfer function and the lag transfer function at any angle, the estimated parameters need to be bilinearly transformed to complete the parameter discretization processing for use in the digital controller.

[0083] The modulation wave is a single-phase signal, and a three-phase signal is constructed by the delay method, that is, by Input generation and , using the SOGI_QSG method, The input is Axis, generated by SOGI_QSG construction transfer function axis data, and then use the trigonometric relationship and , The value of completes the construction of the lead transfer function and the lag transfer function.

[0084] 2) Using the estimated value of the nearest peak before and after the sampling value and the current sampling value, the triangle replacement method is used to solve the intersection point of the modulated wave and the carrier wave by using the similarity relationship of the triangle;

[0085] In the triangular substitution method, the arc between the modulated wave and the carrier is replaced by a straight line BCD at a high carrier frequency, thereby constructing triangle ABC and triangle DCF for calculation to avoid solving transcendental equations. Point A is the peak value of the positive half cycle of the carrier, point B is the intersection of the modulated wave when a perpendicular line is drawn from point A to the time axis, point C is the intersection of the modulated wave and the carrier, point D is the intersection of the modulated wave and the time axis, point E is the peak value of the negative half cycle of the carrier, point F is the intersection of the time axis when a perpendicular line is drawn from point C to the time axis, and point G is the intersection of AE formed by a line drawn along point B and the time axis.

[0086] Figure 2 This is an image composed of a triangular carrier wave and a modulated wave. For a more intuitive calculation, the enlarged image is shown below. Figure 3 As shown, the on-length of PWM is DF, and the off-length of PWM is BG. Here, a replacement is made at a high carrier frequency, and the arc BCD is replaced by the straight line BCD. Therefore, the effective high and low pulse time of PMW can be obtained according to the relationship of the triangle, where the height coordinate of point B is x1, which is the previous input, and the height coordinate of point D is x, which is the current sampling input.

[0087] Depend on Figure 3 It can be seen that there is a triangle ,and , we can get:

[0088] (2)

[0089] (3)

[0090] According to the relationship between equations (2) and (3), equation (4) can be obtained:

[0091] (4).

[0092] 3) Using the relationship between the carrier period and the intersection point, calculate the duty cycle within the carrier period.

[0093] From AB=1–x1, ED=1 + x, BG+DF= / 2, is the carrier period, then the high level time t in the corresponding half cycle can be obtained DF , the calculation result is shown in formula (5):

[0094] (5)

[0095] In order to find the PWM duty cycle within the entire sampling period, the data on the right side of the input data x is analyzed, such as Figure 3 As shown, the modulated wave intersects with the carrier at point H, and the height coordinate of point H is x2. Similarly, the high level time on the right side of the sampling can be calculated:

[0096] (6)

[0097] From the above content, we can know that the high level time of the whole cycle is:

[0098] (7)

[0099] From this, we can also get the low level duration within the cycle:

[0100] (8)

[0101] The PWM waves are maintained in sequence within a PWM cycle Ts. L1 The duration of low level, t H The duration of high level and t L2 The low level of the duration, where t L1 ,t H ,t L2 They are:

[0102]

[0103]

[0104]

[0105] Find t L1 , t H , t L2 The actual value of is the high and low level time within the carrier cycle, where x is the sampling input of the current modulation wave, and x1 is the lead after the lead transfer function calculation. The lead estimate of the angle, x2 is the lag after the lead transfer function is calculated The estimated hysteresis of the angle, t L1 is the first low level time, t H is the high level time, t L2 This is the second low level time.

[0106] A computer device / equipment / system comprises a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the above method.

[0107] A computer-readable storage medium stores a computer program / instruction, which implements the steps of the above method when executed by a processor.

[0108] Example 2

[0109] On the basis of Example 1, according to the obtained high level time and low level time, a digital period register is used to load or increase the value of the register to judge the relationship between the value of the period register and the high and low level time, generate corresponding high and low pulses, and complete the modulation.

[0110] When the per-unit value t of the period counter is less than t L1 The output is low level when t is greater than t L1 and less than t L1 + t H The output is high level, t is greater than t L1 + t H And it is less than Ts, which is a low level, generating the waveform within this period as follows Figure 6 As shown, the processing in other cycles is the same, thereby completing the modulation.

[0111] In this embodiment, a commonly used level converter is used, and its control object is the on-off of the IGBT. The specific implementation method is as follows: Figure 1 As shown, a digital SPWM modulation method of the present embodiment includes a sampling module for sampling a modulation wave, wherein the sampling mode is generally peak sampling, and includes an advance transfer function for solving an estimated value of a sampling value leading a peak value, and includes a lag transfer function for solving an estimated value of a sampling value lagging a peak value; the advance estimated value, the lag estimated value and the current sampling value are brought into the calculation formula derived by the present invention to solve the high and low level time t within the carrier cycle. L1 , t H , t L2 , and then combine the value of the digital cycle register with the relationship between the high and low level time to generate high and low levels to complete the modulation.

[0112] A digital SPWM modulation method of the present invention can avoid solving transcendental equations in modulation calculations and reduce calculation time. The SOGI-QSG type cycle extension transfer function can be used to filter the modulation wave, and the leading and lagging parameters of any angle can be estimated. When used, the transfer function can adjust the parameters according to different carrier frequencies, and has high engineering value. By using a replacement method, the intersection of the modulation wave and the carrier is solved according to the relationship between similar triangles, and then the high and low level times within the carrier cycle are calculated and derived, which improves the accuracy of pulse width modulation compared to the symmetry method.

[0113] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0114] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0115] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0116] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0117] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. A digital SPWM modulation method, characterized in that: include: 1) Sample the modulated wave, obtain the sampled value x as input data, and use the discretized lead transfer function tf1 to obtain the estimated value at the nearest lead peak; Sample the modulated wave, obtain the sampled input x as input data, and use the discretized lag transfer function tf2 to obtain the estimated value at the nearest lag peak; 2) Using the estimated value of the nearest peak before and after the sampling value and the current sampling value, the triangle replacement method is used to solve the intersection point of the modulated wave and the carrier wave by using the similarity relationship of the triangle; 3) Using the relationship between the carrier period and the intersection point, calculate the duty cycle within the carrier period.

2. A digital SPWM modulation method according to claim 1, characterized in that: In step 1), the lead transfer function is a SOGI-QSG type function, and the input data is filtered using the lead transfer function. At the same time, according to the different carrier frequencies, the lead angle is obtained. The estimated value of x1; The complex frequency domain expression of the lead transfer function is: ； in, represents the lead transfer function, k represents the closed-loop coefficient, represents the resonant frequency of SOGI-QSG, represents the complex variable of the Laplace transform.

3. A digital SPWM modulation method according to claim 1, characterized in that: In step 1), the execution process of the lead transfer function is: The input signal x is at the phase-locked angle Perform abc-dq phase coordinate transformation under; After the abc-dq phase coordinate transformation, the signal is Perform dq-bac phase coordinate transformation; The time domain calculation formula of the lead transfer function is: 。 4. A digital SPWM modulation method according to claim 1, characterized in that: In step 1), the hysteresis transfer function is a SOGI-QSG type function, which filters the input data and obtains any hysteresis angle according to the different carrier frequencies. The estimated value x2, the complex frequency domain expression of the lag transfer function is: ； in, represents the hysteresis transfer function, k represents the closed-loop coefficient, represents the resonant frequency of SOGI-QSG, and s represents the complex variable of Laplace transform.

5. A digital SPWM modulation method according to claim 1, characterized in that: The execution process of the hysteresis transfer function is: The input signal x is at the phase-locked angle Perform abc-dq phase coordinate transformation under; After the abc-dq phase coordinate transformation, the signal is Perform dq-bac phase coordinate transformation; The time domain calculation formula of the lag transfer function is: ； After estimating the parameters of the leading transfer function and the lagging transfer function at any angle, the estimated parameters are bilinearly transformed to complete the parameter discretization process for use in the digital controller.

6. A digital SPWM modulation method according to claim 1, characterized in that: In step 2), in the triangular replacement method, the arc between the intersection of the modulated wave and the carrier is replaced by a straight line BCD at a high carrier frequency, thereby constructing triangle ABC and triangle DCF, point A is the peak value of the positive half cycle of the carrier, point B is the intersection point of the modulated wave when a perpendicular line is drawn from point A to the time axis, point C is the intersection point of the modulated wave and the carrier, point D is the intersection point of the modulated wave and the time axis, point E is the peak value of the negative half cycle of the carrier, point F is the intersection point of the time axis when a perpendicular line is drawn from point C to the time axis, and point G is the intersection point formed by a line drawn along point B parallel to the time axis and AE; The on-length of PWM is DF, and the off-length of PWM is BG. At high carrier frequency, the arc BCD is replaced by the straight line BCD. According to the relationship of the triangle, the effective high and low pulse time of PMW is obtained, where the height coordinate of point B is x1, which is the previous input, and the height coordinate of point D is x, which is the current sampling input; There is a triangle ,and ,get: (2) (3) According to the relationship between equations (2) and (3), equation (4) can be obtained: (4)。 7. A digital SPWM modulation method according to claim 1, characterized in that: In step 3), AB=1–x1, ED=1 + x, BG+DF= / 2, is the carrier period, then the high level time t in the corresponding half cycle is obtained DF , the calculation result is shown in formula (5): (5) The modulated wave intersects with the carrier at point H, and the height coordinate of point H is x2. Similarly, the high level time on the right side of the sampling is calculated: (6) The high level time of the whole cycle is: (7) The low level duration within the cycle is obtained: (8) The PWM waves are maintained in sequence within a PWM cycle Ts. L1 The duration of low level, t H The duration of high level and t L2 The low level of the duration, where t L1 ,t H ,t L2 They are: ； ； ； Find t L1 , t H , t L2 The actual value of is the high and low level time within the carrier cycle, where x is the sampling input of the current modulation wave, and x1 is the lead after the lead transfer function calculation. The lead estimate of the angle, x2 is the lag after the lead transfer function is calculated The estimated hysteresis of the angle, t L1 is the first low level time, t H is the high level time, t L2 This is the second low level time.

8. A digital SPWM modulation method according to claim 7, characterized in that: In step 3), according to the obtained high level time and low level time, the digital cycle register is used to judge the relationship between the value of the cycle register and the high and low level time by increasing the value of the register, and the corresponding high and low pulses are generated to complete the modulation.

9. A digital SPWM modulation method according to claim 7, characterized in that: In step 3), when the per-unit value t of the cycle counter is less than t L1 The output is low level when t is greater than t L1 and less than t L1 + t H The output is high level, t is greater than t L1 +t H And it is less than Ts, which is a low level, completing the modulation.

10. A computer device / equipment / system comprising a memory, a processor and a computer program stored in the memory, characterized in that: The processor executes the computer program to implement the steps of the method of claim 1.

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