Pulse width modulation method suitable for photovoltaic inverter

Abstract

The invention relates to the technical field of power electronics, and discloses a pulse width modulation method suitable for a photovoltaic inverter, which comprises the following steps: carrying out sinusoidal processing on an original three-phase modulation signal to obtain a standard three-phase sinusoidal signal; determining a clamping phase according to the boundary size of the standard three-phase sinusoidal signal; according to the determined clamping phase, single-phase modulation signals of the same clamping phase are selected from the original three-phase modulation signals to calculate the actual clamping amount; and adding the actual clamping amount and the original three-phase modulation signal to obtain a corrected three-phase modulation signal. The invention provides a practical modulation strategy, according to the method, the standard sinusoidal signal is used for calculating the clamping phase, three-phase boundary distance comparison is ingeniously converted into standard signal three-phase boundary distance comparison and actual single-phase signal boundary comparison, and the situation that the clamping phase is switched among phases due to modulation signal noise is avoided; the current distortion is reduced; and the system stability is improved.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a pulse width modulation method suitable for a photovoltaic inverter. Background Art

[0002] With the continuous advancement of the national dual-carbon strategy, the promotion and application of new energy is becoming more and more extensive. The country has issued a series of documents to promote the implementation of new energy. Among them, photovoltaic inverters, as important equipment for photovoltaic power generation, have broad market prospects. The function of photovoltaic inverters is to convert the direct current generated by photovoltaics into alternating current. The conversion efficiency and power quality are two important indicators of photovoltaic inverters. At present, the commonly used modulation method for improving efficiency is discrete pulse width modulation strategy (DPWM). DPWMA modulation in the DPWM method is the most widely used. However, in actual applications, this method will have the problem of switching back and forth between clamped phases due to the influence of noise, resulting in insignificant efficiency improvement. A practical DPWM method is urgently needed. Summary of the invention

[0003] In view of the shortcomings and defects of the prior art, the present invention provides a pulse width modulation method suitable for a photovoltaic inverter, which realizes accurate discrimination of the clamping phase, avoids the problem of switching back and forth of the clamping phase caused by noise, reduces current distortion, and improves current THD.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A pulse width modulation method applicable to a photovoltaic inverter, wherein the method is applied to a photovoltaic inverter and comprises the following steps:

[0006] S1, sinusoidalize the original three-phase modulated signal to obtain a standard three-phase sinusoidal signal;

[0007] S2, determining the clamping phase according to the boundary size of the standard three-phase sinusoidal signal;

[0008] S3, according to the determined clamping phase difference, selecting a single-phase modulation signal with the same clamping phase difference from the original three-phase modulation signal to calculate the actual clamping amount;

[0009] S4, adding the actual clamping amount to the original three-phase modulation signal to obtain a modified three-phase modulation signal.

[0010] Preferably, the sinusoidal processing in S1 is to perform a second-order generalized integral filtering process on the original three-phase modulated signal, and its transfer function is:

[0011]

[0012] Where G(s) is the transfer function of the second-order generalized integral, k is 1.414, ω is 314.15, and s is a complex variable;

[0013] The discretization method for the transfer function includes but is not limited to a bilinear transformation method, a zero-order holder method, an impulse response invariance method, a forward difference method, a backward difference method, and a first-order holder method.

[0014] Preferably, in S1, the voltage feedforward component in the original three-phase modulation signal can be used to replace the original three-phase modulation signal for sinusoidal processing.

[0015] Preferably, in S1, part of the components of the original three-phase modulation signal may be used to replace the original three-phase modulation signal for sinusoidal processing.

[0016] Preferably, the method for calculating the actual clamping amount in S3 is:

[0017] First calculate the upper boundary u' of the single-phase modulation signal ph (t) and the lower boundary u′ lh (t):

[0018]

[0019] where u' p (t) is a single-phase modulation signal with the same clamping phase selected from the original three-phase modulation signal according to the determined clamping phase, p represents the phase sequence, p = A or B or C; t is time;

[0020] Then calculate the actual clamping amount V 0 (t):

[0021]

[0022] Preferably, the process of determining the clamping phase in S2 is:

[0023] First calculate the upper boundary u of the standard three-phase sinusoidal signal xh (t) and the lower boundary u xl (t):

[0024]

[0025] Where t is time; u x (t) is a standard three-phase sinusoidal signal, x represents the phase sequence, x = a, b, c;

[0026] Then calculate the minimum value u in the upper and lower boundary data of the standard three-phase sinusoidal signal min :

[0027] u min =min(u ah (t),ubh (t),u ch (t),u al (t),u bl (t),u cl (t));

[0028] Finally, the clamping phase p is obtained according to the following formula:

[0029]

[0030] Preferably, modulation output is performed after the modified three-phase modulation signal is obtained.

[0031] The beneficial technical effect of the present invention is as follows: a practical modulation strategy is proposed, which uses a standard sinusoidal signal to calculate the clamped phase difference, cleverly converting the three-phase boundary distance comparison into the boundary comparison problem of the standard signal three-phase boundary distance comparison and the actual single-phase signal, avoiding the modulation signal noise causing the clamped phase difference to switch between phases, reducing current distortion and improving system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the overall flow chart of the present invention.

[0033] Figure 2 This is the ideal DPWM modulation waveform diagram of the present invention.

[0034] Figure 3 This is a DPWM modulation waveform diagram obtained by using a traditional method in the presence of noise in an embodiment of the present invention.

[0035] Figure 4 This is a DPWM modulation waveform diagram obtained by using the method of the present invention in the presence of noise in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the present invention.

[0037] Embodiment: Combining Figure 1 , a pulse width modulation method suitable for a photovoltaic inverter, comprising the following steps:

[0038] S1, performing sinusoidal processing on the normalized original three-phase modulated signal to obtain a standard three-phase sinusoidal signal;

[0039] S2, determining the clamping phase according to the boundary size of the standard three-phase sinusoidal signal;

[0040] S3, according to the determined clamping phase difference, selecting a single-phase modulation signal with the same clamping phase difference from the original three-phase modulation signal to calculate the actual clamping amount;

[0041] S4, adding the actual clamping amount to the original three-phase modulation signal to obtain a modified three-phase modulation signal.

[0042] Furthermore, the sinusoidal processing in S1 is to perform a second-order generalized integral (SOGI) filtering process on the original three-phase modulated signal, and its transfer function is:

[0043]

[0044] Where G(s) is the transfer function of the second-order generalized integral, k is 1.414, ω is 314.15, s is a complex variable, and the transfer function is discretized using the bilinear transformation method (sampling frequency 30kHz), and the obtained discrete transfer function is:

[0045]

[0046] Where G(z) is the discrete transfer function of SOGI, u' x (z) is the original three-phase modulation signal u' x (t) is the z-transformation, ux(z) is the standard three-phase sinusoidal signal u obtained after SOGI x z-transform of (t).

[0047] Furthermore, the process of determining the clamping phase difference in S2 is:

[0048] First calculate the upper boundary u of the standard three-phase sinusoidal signal xh (t) and the lower boundary u xl (t):

[0049]

[0050] Where t is time; u x (t) is a standard three-phase sinusoidal signal, x represents the phase sequence, x = a, b, c;

[0051] Then calculate the minimum value u in the upper and lower boundary data of the standard three-phase sinusoidal signal min :

[0052] u min =min(u ah (t),u bh (t),u ch (t),u al (t),u bl (t),u cl (t));

[0053] Finally, the clamping phase p is obtained according to the following formula:

[0054]

[0055] Furthermore, the method for calculating the actual clamping amount in S3 is:

[0056] First calculate the upper boundary u' of the single-phase modulation signal ph (t) and the lower boundary u l ' h (t):

[0057]

[0058] where u' p (t) is a single-phase modulation signal with the same clamping phase selected from the original three-phase modulation signal according to the determined clamping phase, p represents the phase sequence, p = A or B or C; t is time;

[0059] Then calculate the actual clamping amount V 0 (t):

[0060]

[0061] Furthermore, the modified three-phase modulation signal u″ is obtained in S4 x (t) is to set the actual clamping value V 0 (t) Make zero sequence quantity and original three-phase modulation signal u' x (t) directly add to get:

[0062] u″ x (t) = u' x (t)+V 0 (t).

[0063] The modified three-phase modulation signal can be used as a modulation signal for modulation output. Figure 2 For the ideal modulation output, Figure 3 and Figure 4 For actual modulation output, combined with Figure 3 and Figure 4 It can be seen that this method can effectively avoid clamped phase switching.

[0064] The above embodiments are descriptions of specific implementation methods of the present invention rather than limitations of the present invention. Technical personnel in the relevant technical field may make various changes and modifications to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A pulse width modulation method suitable for a photovoltaic inverter, characterized in that: The method is applied to a photovoltaic inverter and comprises the following steps: S1, sinusoidalize the original three-phase modulated signal to obtain a standard three-phase sinusoidal signal; S2, determining the clamping phase according to the boundary size of the standard three-phase sinusoidal signal; S3, according to the determined clamping phase difference, selecting a single-phase modulation signal with the same clamping phase difference from the original three-phase modulation signal to calculate the actual clamping amount; S4, adding the actual clamping amount to the original three-phase modulation signal to obtain a modified three-phase modulation signal.

2. A pulse width modulation method suitable for a photovoltaic inverter according to claim 1, characterized in that: The sinusoidal processing in S1 is to perform a second-order generalized integral filtering process on the original three-phase modulated signal, and its transfer function is: Where G(s) is the transfer function of the second-order generalized integral, k is 1.414, ω is 314.15, and s is a complex variable; The discretization method for the transfer function includes but is not limited to a bilinear transformation method, a zero-order holder method, an impulse response invariance method, a forward difference method, a backward difference method, and a first-order holder method.

3. A pulse width modulation method suitable for a photovoltaic inverter according to claim 1, characterized in that: In S1, the voltage feedforward component in the original three-phase modulation signal can be used to replace the original three-phase modulation signal for sinusoidal processing.

4. A pulse width modulation method suitable for a photovoltaic inverter according to claim 1, characterized in that: In S1, part of the components of the original three-phase modulation signal may be used to replace the original three-phase modulation signal for sinusoidal processing.

5. A pulse width modulation method suitable for a photovoltaic inverter according to claim 1, characterized in that: The method for calculating the actual clamping amount in S3 is: First calculate the upper boundary u' of the single-phase modulation signal ph (t) and the lower boundary u l ' h (t): where u' p (t) is a single-phase modulation signal with the same clamping phase selected from the original three-phase modulation signal according to the determined clamping phase, p represents the phase sequence, p = A or B or C; t is time; Then calculate the actual clamping amount V0(t):

6. A pulse width modulation method suitable for a photovoltaic inverter according to claim 1, characterized in that: The process of determining the clamping phase in S2 is as follows: First calculate the upper boundary u of the standard three-phase sinusoidal signal xh (t) and the lower boundary u xl (t): Where t is time; u x (t) is a standard three-phase sinusoidal signal, x represents the phase sequence, x = a, b, c; Then calculate the minimum value u in the upper and lower boundary data of the standard three-phase sinusoidal signal min : u min =min(u ah (t),u bh (t),u ch (t),u al (t),u bl (t),u cl (t); Finally, the clamping phase p is obtained according to the following formula:

7. A pulse width modulation method suitable for a photovoltaic inverter according to claim 1, characterized in that: After the modified three-phase modulation signal is obtained, modulation output is performed.

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