Multi-target alternating current waveform unnotched shaping method

Abstract

The invention relates to a multi-target alternating current waveform unnotched shaping method, which is suitable for an AC-DC rectifier and a DC-AC inverter of which the direct current side voltage is greater than the amplitude of the alternating current side voltage. In order to consider a plurality of indexes such as PF, THDi, each harmonic current limit value, CF, WF, AF and the like, on the basis of single odd-number harmonic injection, a multi-segment broken line form is adopted to describe an alternating current reference of an alternating current control loop implanted into the power electronic device. By connecting specific end points, an alternating current reference can be quickly constructed, the requirements of PF, THDi and each harmonic current limiting value are met firstly, and then better CF, WF and AF expressions can be obtained through optimization.

Description

Technical Field

[0001] This invention relates to a method for shaping the AC side current waveform of power electronic devices to meet multiple objective requirements, particularly a method for shaping the current waveform without gaps on the input side of an AC-DC rectifier and the output side of a DC-AC inverter, which can adapt to the needs of different applications. Background Technology

[0002] When alternating current is distorted, its harmonics not only reduce the efficiency of power production, transmission and utilization, but also cause problems such as overheating of electrical equipment, vibration and noise, insulation aging, shortened service life, failure and burnout. Furthermore, they can interfere with the normal operation of electrical equipment used in detection, communication, medical, transportation and processing.

[0003] The more an alternating current deviates from a standard sinusoidal waveform, the more severe its harmonic hazards. To provide a reference for harmonic control, a series of standards and specifications related to power factor (PF), total current distortion (THDi), and harmonic current limits have been introduced. AC-DC rectifiers and DC-AC inverters are typical power electronic devices, and their AC-side currents also need to meet these standards. Existing harmonic injection methods can improve the harmonic performance of the AC-side current in power electronic devices. Injecting specific orders of harmonics into the AC current control loop can increase PF and reduce the harmonic current amplitude and THDi.

[0004] However, besides harmonic characteristics, the AC current of power electronic devices also needs to consider parameters such as crest factor (CF), waveform factor (WF), and averaging factor (AF). The CF value of a standard sine wave is... WF value AF value Generally speaking, the lower the values ​​of CF, WF, and AF, the smaller the instantaneous current that the power electronic device needs to withstand, and the smaller the fluctuation of its instantaneous power. Therefore, the current waveform on the AC side of the power electronic device not only needs to meet multiple target values ​​simultaneously (such as PF, THDi, various harmonic current limits, CF, WF, AF, etc.), but also needs to be further optimized if multiple feasible solutions exist.

[0005] For AC-DC rectifiers and DC-AC inverters where the DC side voltage is greater than the AC side voltage amplitude, the current waveform on their AC side can easily achieve "gap-free" (i.e., "dead zone-free"), making them easier to manage. Summary of the Invention

[0006] For AC-DC rectifiers and DC-AC inverters where the DC side voltage is greater than the AC side voltage amplitude, in order to overcome the shortcomings of existing harmonic injection methods that focus on improving harmonic performance, this invention proposes a multi-objective method for shaping the AC current waveform without gaps.

[0007] Regarding AC side voltage Using Vacm as amplitude and fac as frequency, and taking into account indicators such as PF, THDi, harmonic current limits, CF, WF, and AF, a gapless AC current waveform shaping method with multiple objectives according to an embodiment of the present invention includes the following steps:

[0008] Based on the requirements of PF, THDi, and the limits of each harmonic current, the limit of the ratio of each harmonic current to the fundamental current is corrected. For example, the highest requirement among the three limits of PF, THDi, and each harmonic current can be taken to correct the limit of the ratio of each harmonic current to the fundamental current. The resulting limit of the ratio of each harmonic current to the fundamental current can ensure that the requirements of PF, THDi, and each harmonic current are met simultaneously.

[0009] Constructing a harmonic injection current normalized to the fundamental frequency h is a positive odd number greater than 1, and the parameter b satisfies: During this period, at any time The instantaneous power fluctuation rate s_pac_norm(t) ≤ ε, where ε is a quantity greater than 0, and s_pac_norm(t) can be defined as... or or etc., used to characterize the degree of fluctuation of instantaneous power pac_norm(t), instantaneous power Average power pac_norm_max is The maximum value of pac_norm(t) during the period, pac_norm_min is The minimum value of pac_norm(t) during the period; the initial value of h can be set to the harmonic order corresponding to the larger value among the limit values ​​of the ratio of each harmonic current to the fundamental current, generally 3, 5, or 7; if If the initial value of b is greater than 0, then the initial value of b is less than 0, and the period Tac = 1 / fac;

[0010] Based on the harmonic injection current normalized to the fundamental frequency, an AC current reference iac_ref(t) is constructed, with a period equal to Tac. It is centrally symmetric at time t = Tac / 2 and y-symmetric at t = Tac / 4. period:

[0011] iac_ref(t) is a polyline with m segments, where m is a positive integer and Using (0, 0), (tr, iac_norm(tr)), (Tac / 4, iac_norm(tr)) and any (m-2) points conforming to (tj, iac_norm(tj)) as endpoints, connect them in chronological order to form iac_ref(t), time... j is a positive integer and 0 < tj < tr;

[0012] If the ratio of each harmonic current to the fundamental current in the AC current reference iac_ref(t) is less than the limit for the ratio of each harmonic current to the fundamental current, then it is incorporated into the AC current control loop of the power electronic device, for example, as an AC current reference for AC current waveform shaping; otherwise, adjust parameters b, ε, m, and h until the ratio of each harmonic current to the fundamental current in the AC current reference iac_ref(t) is less than the limit for the ratio of each harmonic current to the fundamental current. Trial and error methods and perturbation methods can be used to adjust the above parameters.

[0013] According to an embodiment of the present invention, in order to improve the CF, WF and AF performance of the AC side current of the power electronic device, an optimization function f_opt(CF, WF, AF) can be defined, for example: f_opt(CF, WF, AF) = CF or WF or AF, and its optimal value is the minimum value;

[0014] Replace (tr, iac_norm(tr)) with (tra, iac_norm(tra)) and replace (Tac / 4, iac_norm(tr)) with (Tac / 4, iac_norm(tra)), while keeping the other endpoints unchanged. At time tra, 0 < tra ≤ tr.

[0015] The reconstructed AC current reference iac_ref(t) still has a period equal to Tac, remains centrally symmetric at time t = Tac / 2, and remains y-symmetric at t = Tac / 4. period:

[0016] iac_ref(t) is still a polyline with m segments, where m is a positive integer and Using (0, 0), (tra, iac_norm(tra)), (Tac / 4, iac_norm(tra)), and any (m-2) points conforming to (tj, iac_norm(tj)) as endpoints, reconnect them in chronological order to form iac_ref(t), at time... j is a positive integer and 0 < tj < tr;

[0017] Based on the requirement that the ratio of each harmonic current to the fundamental current still needs to be satisfied by iac_ref(t), the range of values ​​for tra is determined; the initial value of tra can be set to tr; by changing tra, the range of values ​​for tra can be obtained by stepping.

[0018] Within the range of values ​​of tra, the iac_ref(t) corresponding to the optimal value of the optimization function is taken as the optimized AC current reference iac_ref_opt(t), and it is embedded into the AC current control loop of the power electronic device, such as: as an AC current reference for AC current waveform shaping.

[0019] According to an embodiment of the present invention, in order to improve the CF, WF, and AF performance of the AC side current of the power electronic device, iac_ref(t) can also be directly modified by replacing (tr, iac_norm(tr)) with (trb, iac_norm(trb)) and replacing (Tac / 4, iac_norm(tr)) with (Tac / 4, iac_norm(trb)), while keeping the other endpoints unchanged. At time trb, the following condition is met:

[0020] Either iac_norm_min or iac_norm_max, where iac_norm_max is... The maximum value of iac_norm(t) during the period, iac_norm_min is The minimum value of iac_norm(t) during the period, 0 < trb < tr;

[0021] The modified AC current reference iac_ref(t) retains a period equal to Tac, remains centrally symmetric at time t = Tac / 2, and exhibits y-axis symmetry at t = Tac / 4. period:

[0022] iac_ref_imp(t) is still a polyline with m segments, where m is a positive integer and Using (0, 0), (trb, iac_norm(trb)), (Tac / 4, iac_norm(trb)), and any (m-2) points conforming to (tj, iac_norm(tj)) as endpoints, reconnect them in chronological order to form iac_ref_imp(t), at time... j is a positive integer and 0 < tj <tr;

[0023] If the ratio of each harmonic current to the fundamental current of iac_ref_imp(t) is less than the limit of the ratio of each harmonic current to the fundamental current, then it is embedded in the AC current control loop of the power electronic device, such as as an AC current reference for AC current waveform shaping.

[0024] The beneficial effects of this invention are mainly reflected in the following aspects: it can take into account multiple indicators such as PF, THDi, harmonic current limits, CF, WF, and AF. Based on the h-th harmonic injection, it uses an m-segment piecewise linear form to describe the AC current reference of the AC current control loop embedded in the power electronic device. In digital control, storing one m-segment piecewise linear line only requires information from (m+1) endpoints, occupying a small number of registers. Moreover, in the process of quickly determining the AC current reference, there are multiple optional parameter combination schemes, providing room for optimization. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of Embodiment 1 of the present invention;

[0027] Figure 2 This is a schematic diagram of the normalized fundamental current, iac_norm, and pac_norm in Embodiment 1 of the present invention (with h = 5).

[0028] Figure 3 This is a schematic diagram of iac_norm and iac_ref in Embodiment 1 of the present invention (with h = 5, ε = 0.01, b = -0.1 and m = 2).

[0029] Figure 4 This is a spectrum of the ratio of each harmonic current to the fundamental current in iac_ref according to Embodiment 1 of the present invention (with h = 5, ε = 0.01, b = -0.1 and m = 2).

[0030] Figure 5 This is a schematic diagram of iac_norm and iac_ref in Embodiment 1 of the present invention (with h = 5, ε = 0.01, b = -0.1 and m = 3).

[0031] Figure 6 This is a spectrum of the ratio of each harmonic current to the fundamental current in iac_ref according to Embodiment 1 of the present invention (with h = 5, ε = 0.01, b = -0.1 and m = 3).

[0032] Figure 7 This is an optimized sub-flowchart of Embodiment 2 of the present invention;

[0033] Figure 8This is a schematic diagram of iac_norm and iac_ref_opt in Embodiment 2 of the present invention (with h = 5, ε = 0.01, b = -0.1 and m = 2).

[0034] Figure 9 This is the spectrum of the ratio of each harmonic current to the fundamental current in iac_ref_opt according to Embodiment 2 of the present invention (with h = 5, ε = 0.01, b = -0.1 and m = 2).

[0035] Figure 10 This is a schematic diagram of iac_norm and iac_ref_imp in Embodiment 3 of the present invention (with h = 5, ε = 0.01, b = -0.1 and m = 2).

[0036] Figure 11 This is the spectrum of the ratio of each harmonic current to the fundamental current in iac_ref_imp according to Embodiment 3 of the present invention (with h = 5, ε = 0.01, b = -0.1 and m = 2). Detailed Implementation

[0037] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0038] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0039] Example 1

[0040] A Boost PFC circuit is an AC-DC rectifier where the DC-side voltage is greater than the AC-side voltage amplitude, and its input current waveform is seamless. Taking it as an example, its input voltage... Vacm is the amplitude, fac is the frequency, and the output voltage Vdc > Vacm. The following conditions must be met: power factor PF >= PF0, total current distortion THDi <= THDi0, effective value of nth harmonic current Iacn <= Iacn0, where n is a positive integer and n > 1, 0 ≤ PF0 ≤ 1, THDi0 ≥ 0%, and Iacn0 ≥ 0.

[0041] like Figure 1As shown, a suitable method for non-gap shaping of AC current waveforms for multiple objectives includes the following steps:

[0042] The relationship between THDi and Iacn satisfies equation (1), where Iac1 is the effective value of the fundamental current; when the phase factor DPF in PF is 1, the relationship between THDi and PF satisfies equation (2).

[0043] (1)

[0044] (2)

[0045] Based on equations (1) and (2), after conversion, the most stringent requirement among PF ≥ PF0, THDi ≤ THDi0, and Iacn ≤ Iacn0 is taken to correct the limit value of the ratio of each harmonic current to the fundamental current, Iacn_lim / Iac1. After correction, Iacn_lim <= Iacn0.

[0046] Define instantaneous power fluctuation rate Take the fundamental wave and the h-th harmonic, such as Figure 2 The diagram shows the construction of a harmonic injection current normalized to the fundamental frequency. h is a positive odd number greater than 1, and the parameter b satisfies: During this period, at any time s_pac_norm(t) ≤ ε, where ε is a quantity greater than 0, representing the instantaneous power. Average power Tac is the period.

[0047] like Figure 3 As shown, based on iac_norm(t), an AC current reference iac_ref(t) is constructed. Its period is equal to Tac, and it is centrally symmetric at time t = Tac / 2 and y-symmetric at t = Tac / 4. During: iac_ref(t) is a polyline with m segments, where m is a positive integer and The m segments of the polyline are connected sequentially in chronological order to the following (m+1) endpoints: (0, 0), (tr, iac_norm(tr)), (Tac / 4, iac_norm(tr)), and any (m-2) points conforming to (tj, iac_norm(tj)), at time... j is a positive integer and 0 < tj < tr.

[0048] For clarity, assume PF0 = 0.9, THDi0 = 20%, and that all harmonic current limits comply with the Class C standard of IEC 61000-3-2. Calculations show that THDi ≤ 20% is the most stringent of the three, with the following corrections: Iac3_lim / Iac1 = 0.1, Iac5_lim / Iac1 = 0.07, while the remaining ratio limits remain the same as the Class C standard of IEC 61000-3-2.

[0049] Let h = 5, ε = 0.01, b = -0.1 and m = 2, as follows Figure 4 As shown, the ratios of each harmonic current to the fundamental current in the obtained iac_ref(t) are all less than the limit for the ratio of each harmonic current to the fundamental current, and PF ≈ 0.9974, THDi ≈ 7.165%, CF ≈ 1.464, WF ≈ 1.139, and AF ≈ 1.667, which meet the requirements. Therefore, it can be implanted into the AC current control loop of the Boost PFC circuit as an AC current reference for AC current waveform shaping.

[0050] Let h = 5, ε = 0.01, b = -0.1, and m = 3. Figure 5 The diagram shows iac_norm(t) and iac_ref(t); as shown... Figure 6 As shown, the ratios of each harmonic current to the fundamental current in the obtained iac_ref(t) are all less than the limits for the ratio of each harmonic current to the fundamental current: PF ≈ 0.9999, THDi ≈ 1.541%, CF ≈ 1.390, WF ≈ 1.112, and AF ≈ 1.545, which meet the requirements. Moreover, all performance parameters are superior to those of m = 2. It can also be embedded in the AC current control loop of the Boost PFC circuit as an AC current reference for AC current waveform shaping.

[0051] Other parameter combinations (h, ε, b, m) have similar effects, which will not be elaborated further.

[0052] Example 2

[0053] Using a parameter combination (h = 5, ε = 0.01, b = -0.1, and m = 2), Example 1 was optimized to improve its CF, WF, and AF performance. An optimization function f_opt(CF, WF, AF) = CF was defined, with the optimized value being the minimum.

[0054] like Figure 7 As shown, a suitable method for non-gap shaping of AC current waveforms with multiple objectives includes the following optimization steps:

[0055] Replace (tr, iac_norm(tr)) with (tra, iac_norm(tra)) and replace (Tac / 4, iac_norm(tr)) with (Tac / 4, iac_norm(tra)), while keeping the other endpoints unchanged. At time tra, 0 < tra ≤ tr.

[0056] The reconstructed AC current reference iac_ref(t) still has a period equal to Tac, remains centrally symmetric at time t = Tac / 2, and remains y-symmetric at t = Tac / 4. period:

[0057] iac_ref(t) is still a polyline with m segments, where m is a positive integer and The m segments of the broken line are connected sequentially in time to the following (m+1) endpoints: (0, 0), (tra, iac_norm(tra)), (Tac / 4, iac_norm(tra)), and any (m-2) points conforming to (tj, iac_norm(tj)), at time... j is a positive integer and 0 < tj < tr;

[0058] Based on the requirement that the ratio of each harmonic current to the fundamental current still needs to be satisfied by iac_ref(t), the range of values ​​for tra is determined; the initial value of tra can be set to tr; by changing tra, the range of values ​​for tra can be obtained by stepping.

[0059] Within the range of values ​​for tra, the optimal AC current reference iac_ref(t) corresponding to the optimal value of the optimization function is taken as iac_ref_opt(t).

[0060] Figure 8 The figures shown are iac_norm(t) and iac_ref_opt(t), with tra approximately 0.129 Tac; as Figure 9 As shown, the optimal value of f_opt(CF, WF, AF) is 1.235. The ratios of each harmonic current to the fundamental current in the obtained iac_ref_opt(t) are all less than the limit values ​​for the ratios of each harmonic current to the fundamental current: PF ≈ 0.9938, THDi ≈ 11.18%, CF ≈ 1.235, WF ≈ 1.092, and AF ≈ 1.348, which meets the requirements. Moreover, the performance of CF, WF, and AF is better than that of Example 1. They can be implanted into the AC current control loop of the Boost PFC circuit as an AC current reference for AC current waveform shaping.

[0061] Example 3

[0062] Using the same parameter combination (h = 5, ε = 0.01, b = -0.1 and m = 2), Example 1 was modified to improve the CF, WF and AF performance of Example 1.

[0063] Replace (tr, iac_norm(tr)) with (trb, iac_norm(trb)), replace (Tac / 4, iac_norm(tr)) with (Tac / 4, iac_norm(trb)), and keep the other endpoints unchanged. At time trb, the following condition is met:

[0064] iac_norm_max is The maximum value of iac_norm(t) during the period, iac_norm_min is The minimum value of iac_norm(t) during the period, 0 < trb < tr;

[0065] The modified AC current reference iac_ref(t) retains a period equal to Tac, remains centrally symmetric at time t = Tac / 2, and exhibits y-axis symmetry at t = Tac / 4. period:

[0066] iac_ref_imp(t) is still a polyline with m segments, where m is a positive integer and The m segments of the broken line are connected sequentially in chronological order to the following (m+1) endpoints: (0, 0), (trb, iac_norm(trb)), (Tac / 4, iac_norm(trb)), and any (m-2) points conforming to (tj, iac_norm(tj)), at time... j is a positive integer and 0 < tj <tr。

[0067] Figure 10 The diagram shows iac_norm(t) and iac_ref_imp(t); as shown Figure 11 As shown, the ratios of each harmonic current to the fundamental current in the obtained iac_ref_imp(t) are all less than the limits for the ratio of each harmonic current to the fundamental current: PF ≈ 0.9984, THDi ≈ 5.642%, CF ≈ 1.312, WF ≈ 1.111, and AF ≈ 1.458, which meet the requirements. Moreover, all performance values ​​are superior to those in Example 1. It can be embedded in the AC current control loop of the Boost PFC circuit as an AC current reference for AC current waveform shaping.

[0068] In addition, time trb can also correspond to Alternatively, iac_norm_min can be used, with similar effects, so I won't go into details.

[0069] In summary, the Boost PFC circuit in the embodiments can be replaced by a Buck-type grid-connected inverter circuit, a DC-AC inverter where the DC-side voltage is greater than the AC-side voltage amplitude. In the application of the inverter circuit, the AC current reference can be used as the modulation wave in SPWM control for AC current waveform shaping.

[0070] In addition to Boost PFC circuits and Buck-type grid-connected inverter circuits, this invention is also applicable to other AC-DC rectifiers and DC-AC inverters with no gaps in the AC side current waveform.

[0071] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A gapless waveform shaping method for AC current with multiple objectives, applicable to AC-DC rectifiers or DC-AC inverters where the DC-side voltage is greater than the AC-side voltage amplitude, and the AC-side voltage is... ;in, Vacm is the amplitude and fac is the frequency. The method is characterized by including the following steps: Based on the requirements of PF, THDi, and the limits of each harmonic current, the limit of the ratio of each harmonic current to the fundamental current is modified. Constructing a harmonic injection current normalized to the fundamental frequency Where h is a positive odd number greater than 1, and b satisfies: During this period, at any time The instantaneous power fluctuation rate s_pac_norm(t) ≤ ε, where ε is a quantity greater than 0, and the period Tac = 1 / fac; Construct an AC current reference iac_ref(t) with a period equal to Tac, exhibiting central symmetry at time t = Tac / 2 and y-axis symmetry at t = Tac / 4. period: The AC current reference iac_ref(t) is a piecewise linear function with m segments, where m is a positive integer and The m segments of the polyline are connected sequentially in chronological order to the following (m+1) endpoints: (0, 0), (tr, iac_norm(tr)), (Tac / 4, iac_norm(tr)), and any (m-2) points conforming to (tj, iac_norm(tj)), at time... j is a positive integer and 0 < tj <tr; If the ratio of each harmonic current to the fundamental current of the AC current reference iac_ref(t) is less than the limit of the ratio of each harmonic current to the fundamental current, then it is implanted into the AC current control loop of the power electronic device; otherwise, adjust b, ε, m and h until the ratio of each harmonic current to the fundamental current of the AC current reference iac_ref(t) is less than the limit of the ratio of each harmonic current to the fundamental current.

2. The method for non-gap shaping of AC current waveforms for multiple targets as described in claim 1, characterized in that: It also includes initialization methods for h and b, setting the initial value of h to be equal to the harmonic order corresponding to the larger of the ratio limits between each harmonic current and the fundamental current; if If the initial value of b is greater than 0, then the initial value of b is greater than 0; otherwise, the initial value of b is less than 0.

3. The method for non-discrete shaping of AC current waveforms for multiple targets as described in claim 1 or 2, characterized in that: It also includes an optimization method, which replaces (tr, iac_norm(tr)) with (tra, iac_norm(tra)) and (Tac / 4, iac_norm(tra)) with (Tac / 4, iac_norm(tr)) based on the AC current reference iac_ref(t), while keeping the other endpoints unchanged, and at time tra, 0 < tra ≤ tr; The reconstructed AC current reference iac_ref(t) still has a period equal to Tac, remains centrally symmetric at time t = Tac / 2, and remains y-symmetric at t = Tac / 4. period; The AC current reference iac_ref(t) is still a single m-segment polyline, where m is a positive integer and The m segments of the broken line are connected sequentially in time to the following (m+1) endpoints: (0, 0), (tra, iac_norm(tra)), (Tac / 4, iac_norm(tra)), and any (m-2) points conforming to (tj, iac_norm(tj)), at time... j is a positive integer and 0 <tj < tr; Based on the requirement that the ratio of each harmonic current to the fundamental current still needs to be satisfied by the AC current reference iac_ref(t), the range of values ​​for tra is determined. Within the range of values ​​of tra, the AC current reference iac_ref(t) corresponding to the optimal value of the optimization function is taken as the optimized AC current reference iac_ref_opt(t), and is embedded into the AC current control loop of the power electronic device. The variables of the optimization function include any combination of CF, WF and AF.

4. The method for non-discrete shaping of AC current waveforms for multiple targets as described in claim 3, characterized in that: It also includes an initialization method for time tra, which sets the initial value of time tra equal to time tr.

5. The method for non-discrete shaping of AC current waveforms for multiple targets as described in claim 1 or 2, characterized in that: It also includes a modification method: based on the AC current reference iac_ref(t), (tr, iac_norm(tr)) is replaced by (trb, iac_norm(trb)), and (Tac / 4, iac_norm(trb)) is replaced by (Tac / 4, iac_norm(tr)), while the other endpoints remain unchanged. At time trb, the following condition is met: Either iac_norm_min or iac_norm_max, where iac_norm_max is... The maximum value of iac_nom(t) during the period, iac_norm_min is The minimum value of iac_norm(t) during the period, 0 < trb < tr; The modified AC current reference iac_ref(t) retains a period equal to Tac, remains centrally symmetric at time t = Tac / 2, and exhibits y-axis symmetry at t = Tac / 4. period; The modified AC current reference iac_ref_imp(t) is still a single m-segment polyline, where m is a positive integer and The m segments of the broken line are connected sequentially in chronological order to the following (m+1) endpoints: (0, 0), (trb, iac_norm(trb)), (Tac / 4, iac_norm(trb)), and any (m-2) points conforming to (tj, iac_norm(tj)), at time... j is a positive integer and 0 < tj < tr; If the ratio of each harmonic current to the fundamental current in the modified AC current reference iac_ref_imp(t) is less than the limit of the ratio of each harmonic current to the fundamental current, then it is implanted into the AC current control loop of the power electronic device.

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