Modulation Wave Reconstruction Method of Discontinuous Space Vector Modulation Based on Carrier Modulation

Abstract

The present invention discloses a modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation, firstly selecting stacked carriers for modulation, and then obtaining an equivalent modulation wave of discontinuous space vector modulation; then adjusting the position of the carrier so that the valley value of the upper carrier of the two adjusted adjacent carriers is greater than the peak value of the lower carrier, and the margins between the two adjusted adjacent carriers are equal, to obtain the adjusted carrier; then reconstructing the equivalent modulation wave to form a virtual modulation wave. This method first adjusts the position of the carrier, and then reconstructs the virtual modulation wave on the basis of the equivalent modulation wave, which can not only ensure that there is sufficient non-contact margin between the valley and the peak of the adjacent carriers, but also the margin size can be adjusted in real time according to the actual working conditions, and will not affect the period of the carrier, and is easy to be extended to the control method of different level converters.

Description

Technical Field

[0001] The invention belongs to the field of multi-level converter PWM control, and in particular relates to a modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation. Background Art

[0002] In recent years, with the rapid development of new energy grid connection, changes in power system structure, and the increasing requirements for converter voltage level, capacity and output quality, traditional two-level converters are restricted by the number of levels and the voltage level of power switching devices, and are increasingly unable to meet the needs of different applications. Multi-level converters have been widely studied and applied due to their advantages such as high withstand voltage level, low output harmonic content, and low output common mode voltage.

[0003] The modulation strategy is the key to the performance of the multi-level converter. It complements the topology of the converter (rectifier / inverter) and largely determines the quality of the converter output waveform and the efficiency of the system. At present, the most widely used are carrier pulse width modulation and space vector pulse width modulation (SVPWM). Compared with carrier pulse width modulation, SVPWM has the advantages of high voltage utilization and low harmonic content and is widely used.

[0004] The implementation of the SVPWM method requires a series of work such as sector judgment, vector selection and action time calculation. As the number of levels increases, the complexity of the SVPWM algorithm increases dramatically and is not suitable for real-time calculation. In order to enable the SVPWM method to be applied to three-level or even higher occasions, many scholars have focused on the basic principles of pulse width modulation and the principle of carrier-based sinusoidal pulse width modulation (SPWM). By studying the internal connection between the two, they have proposed methods such as the unified theory of space vector and carrier modulation strategies.

[0005] In actual SVPWM, due to the need to consider the midpoint balance, switching loss or other performance issues of the multi-level converter, some scholars have studied the switching sequence of multi-level space vector modulation and proposed a variety of discontinuous space vector modulation (DPWM) methods. However, for DPWM, in some switching cycles, there is a phase modulation wave that is exactly at the junction of multiple layers of carriers. When the modulation wave is at the critical point of the adjacent carrier peak and valley, it is easy for the switching device to be mis-conducted, affecting the stability of the multi-level converter operation, especially at high or ultra-high frequencies. To solve this problem, the most common method is to reduce the peak-to-peak value of the carrier so that there is a non-contact margin between the adjacent carrier valley and peak. However, in practice, if the margin is not enough, considering the actual working conditions, the carrier adoption method (co-phase stacking or anti-phase stacking), carrier modulation method, detection and control and other factors, mis-conduction will still occur; if the margin is sufficient, it will affect the peak-to-peak value of the carrier, and then affect the carrier period. Summary of the invention

[0006] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation.

[0007] The technical solution of the present invention to solve the technical problem is to provide a modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation, characterized in that the method comprises the following steps:

[0008] Step 1: According to the number of levels N of the multilevel converter, select N-1 stacked carriers for modulation. Let carrier u ck (k=1,2,3,…,N-1) from top to bottom are u c1 ,u c2 ,u c3 ,…,u c(N-1) ;

[0009] Step 2: According to the principle of SPWM modulation, inject the zero-sequence component to obtain the equivalent modulation wave u of discontinuous space vector modulation mi (i=a,b,c);

[0010] Step 3: Adjust the position of the carrier so that the valley value of the upper carrier among the two adjacent carriers after adjustment is greater than the peak value of the lower carrier, and the margin between the two adjacent carriers after adjustment is △x, and obtain the adjusted carrier u′ ck (k=1,2,3,…,N-1);

[0011] Step 4: Equivalent modulation wave u mi(i=a,b,c) is reconstructed to form a virtual modulation wave u′ mi (i=a,b,c);

[0012] Assume that the carrier u ck The peak value is u cku , the valley value is u ckd , then the virtual modulation wave u′ mi The reconstruction of (i=a,b,c) is as follows:

[0013] When the number of levels N is an odd number: If u ckd <u mi <u cku , then the virtual modulation wave If u mi =u ckd (ie equivalent modulation wave u mi The curve and u ckd The intersecting part), then the virtual modulation wave If u mi =u cku (ie equivalent modulation wave u mi The curve and u cku The intersecting part), then the virtual modulation wave

[0014] When the number of levels N is an even number and the carrier moves up as a whole: If u ckd <u mi <u cku , then the virtual modulation wave u′ mi =u mi +(N-1-k)Δx; if u mi =u ckd , then the virtual modulation wave u′ mi =u mi +(N-1.5-k)Δx; if u mi =u cku , then the virtual modulation wave u′ mi =u mi +(N-0.5-k)Δx;

[0015] When the number of levels N is an even number and the carrier moves downward as a whole: if u ckd <u mi <u cku , then the virtual modulation wave u′ mi =u mi -(k-1)Δx; if u mi =u ckd , then the virtual modulation wave u′ mi =u mi -(k-1.5)Δx; if u mi =u cku, then the virtual modulation wave u′ mi =u mi -(k-2.5)Δx.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention first adjusts the position of the carrier wave, and then reconstructs the virtual modulation wave based on the equivalent modulation wave. This not only ensures that there is sufficient non-contact margin between the troughs and peaks of adjacent carrier waves, the size of the margin can be adjusted in real time according to actual working conditions, and will not affect the period of the carrier wave. It is also easy to expand to the control method of converters with different levels.

[0018] (2) The carrier in the present invention only changes its position but does not change its peak-to-peak value, thus not affecting the period of the carrier.

[0019] (3) The method of reconstructing virtual modulation waves of the present invention is not only easy to expand to different levels of DPWM, but also can provide a reference method for improving the system stability based on the carrier stacking modulation method.

[0020] (4) The present invention performs carrier modulation on the virtual modulation wave and the adjusted carrier wave, which can reliably and effectively obtain the switching sequence, thereby greatly improving the stability of the system. In particular, at high frequency or ultra-high frequency, the stability improvement effect is more obvious.

[0021] (5) The method proposed in the present invention is not affected by factors such as the carrier adoption method (in-phase stacking or anti-phase stacking) and the carrier comparison method, and is conducive to the study of DPWM strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 4 is a main circuit topology diagram of a diode-clamped three-level inverter according to Embodiment 1 of the present invention;

[0023] Figure 2 This is a waveform diagram of the A-phase equivalent modulation wave of the discontinuous space vector modulation according to Embodiment 1 of the present invention;

[0024] Figure 3 This is a schematic diagram of carrier modulation performed by an equivalent modulation wave and a carrier according to Embodiment 1 of the present invention;

[0025] Figure 4 This is a waveform diagram of the adjusted carrier according to Embodiment 1 of the present invention;

[0026] Figure 5 is a waveform diagram of a virtual modulation wave according to Embodiment 1 of the present invention;

[0027] Figure 6 This is a schematic diagram of carrier modulation performed by a virtual modulation wave and an adjusted carrier according to Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the claims of this application.

[0029] The present invention provides a modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation (hereinafter referred to as method), characterized in that the method comprises the following steps:

[0030] Step 1: According to the level number N of the multilevel converter (i.e., three-phase multilevel converter), select N-1 stacked carriers (in-phase stacking or anti-phase stacking) for modulation. Let carrier u ck (k=1,2,3,…,N-1) from top to bottom are u c 1,u c 2,u c 3,…,u c(N-1) ;

[0031] Step 2: According to the principle of SPWM modulation, a specific zero-sequence component is injected into the SPWM sinusoidal modulation wave to obtain the equivalent modulation wave u of discontinuous space vector modulation. mi (i=a,b,c) is u ma 、u mb and u mc ;

[0032] Step 3: Adjust the position of the carrier so that the valley value of the upper carrier among the two adjacent carriers after adjustment is greater than the peak value of the lower carrier, and the margin between the two adjacent carriers after adjustment (the margin is the distance between the valley value of the upper carrier and the peak value of the lower carrier among the two adjacent carriers after adjustment) is △x, and the adjusted carrier u′ is obtained. ck (k=1,2,3,…,N-1);

[0033] Preferably, in step 3, for different level numbers, the corresponding carrier is adjusted as follows:

[0034] Method 1: When the number of levels N is an odd number, the number of carriers is an even number, respectively The carriers located above and below the middle position; the carriers located above the middle position are moved upward relative to their original positions. The adjusted carrier The carriers below the center position are shifted downward relative to their original positions. The adjusted carrier Therefore, the margins between two adjacent carriers after adjustment are equal to △x, and the adjusted carrier

[0035] Method 2: When the number of levels N is an even number, the number of carriers is an odd number, except for the top carrier u c1 Or the lowest carrier u c(N-1) In addition, all carriers are moved up or down, so that the margin between two adjacent carriers after adjustment is △x; specifically: when u c(N-1) Keep it still, when the remaining carrier moves up, the adjusted carrier u′ ck =u ck +(N-1-k)Δx; when u c1 Keep it still, when the remaining carrier moves down, the adjusted carrier ' ck =u ck -(k-1)Δx;

[0036] Step 4: Equivalent modulation wave u mi (i=a,b,c) is reconstructed to form a virtual modulation wave u′ mi (i=a,b,c) is u′ ma , u′ mb and u′ mc ;

[0037] Due to different carrier adjustment methods, the virtual modulation wave reconstruction method is also different; let the carrier u ck The peak value is u cku (Its value is equal to u c(k-1)d ), the valley value is u ckd (Its value is equal to u c(k+1)u ), then the virtual modulation wave u′ mi The specific reconstruction method of (i=a,b,c) is as follows:

[0038] Method 1: When the number of levels N is an odd number, if u ckd <u mi <u cku (ie equivalent modulation wave u mi The curve is located at u ckd and u cku The part between and not including the endpoints), then the virtual modulation wave If u mi =u ckd (ie equivalent modulation wave u mi The curve and u ckd The intersecting part), then the virtual modulation wave If u mi =u cku (ie equivalent modulation wave u mi The curve and u cku The intersecting part), then the virtual modulation wave

[0039] Method 2: When the number of levels N is an even number and the carrier moves up as a whole, if u ckd <u mi <u cku , then the virtual modulation wave u′ mi =u mi +(N-1-k)Δx; if u mi =u ckd , then the virtual modulation wave u′ mi =u mi +(N-1.5-k)Δx; if u mi =u cku , then the virtual modulation wave u′ mi =u mi +(N-0.5-k)Δx;

[0040] When the number of levels N is an even number and the carrier moves downward as a whole, if u ckd <u mi <u cku , then the virtual modulation wave u′ mi =u mi -(k-1)Δx; if u mi =u ckd , then the virtual modulation wave u′ mi =u mi -(k-1.5)Δx; if u mi =u cku , then the virtual modulation wave u′ mi =u mi -(k-2.5)Δx.

[0041] Preferably, the method further comprises step 5, carrier modulation: the virtual modulation wave u′ obtained in step 4 is modulated mi (i=a,b,c)(i.e. u′ ma , u′ mb , u′ mc ) and the adjusted carrier u′ obtained in step 3 ck (k=1,2,3,…,N-1)(i.e. u′ c1 ,u′ c2 ,…,u′ c(N-1) ) is used to perform carrier modulation to obtain an equivalent switching signal.

[0042] Example 1

[0043] Taking a diode clamped three-level inverter as an example, its main circuit topology is as follows: Figure 1 shown. Figure 1 Medium S i1 , S i3 The switch signals of (i=a,b,c) are complementary, S i2 , S i4The switching signals are complementary.

[0044] In step 1, the number of levels N is 3, and two co-phase stacked carriers u are selected. c1 、u c2 , the frequency corresponding to the carrier is 100kHz.

[0045] In step 2, there are many discontinuous space vector modulation methods. Select one of the basic discontinuous space vector modulation methods. Its A phase equivalent modulation wave is as follows: Figure 2 shown. Figure 2 in, u a is the sinusoidal modulation wave in SPWM modulation, u z is the injected zero-sequence component, u ma It is the equivalent modulation wave of DPWM. Figure 2 It can be seen that within one power frequency cycle, u ma The time width between the clamped two carriers is 2△T1, and the switching frequency is 100kHz, so there are more switching cycles between 2△T1. The schematic diagram of the three-phase equivalent modulation wave and the carrier for carrier modulation in one switching cycle is as follows: Figure 3 shown. Figure 3 in, u c1u 、u c1d u c1 The peak and valley values ​​of u c2u 、u c2d u c2 peak and valley values.

[0046] Through carrier modulation, the switch signals of tube 1 and tube 2 of each phase are obtained. When the dead zone is not considered, since tube 1 and tube 3 are complementary, and tube 2 and tube 4 are complementary, the switch signals of the four switch devices of each phase can be obtained. Figure 3 As shown, due to u ma Just in u c1 、u c2 At the junction of the carrier, the carrier passes through u c1d (i.e. u c2u ), considering the factors such as the carrier wave adoption method (in-phase stacking or anti-phase stacking), carrier modulation method, detection and control under actual working conditions, it is easy for the switching device to malfunction, affecting the output quality of the waveform and the stability of the system.

[0047] Therefore, according to step 3, the position of the carrier needs to be adjusted first. Since the number of carriers in this embodiment is small, the margin △x is set to 0.2. The number of levels N = 3 is an odd number, so the carrier u located at the top c1 Move upward by 0.1 as a whole to obtain the adjusted carrier u′ c1 Between 0.1 and 1.1; the carrier u below c2Move down by 0.1 as a whole to get the adjusted carrier u′ c2 Between -0.1 and -1.1.

[0048] Then, according to step 4, the virtual modulation wave is reconstructed. The number of levels N = 3 is an odd number and needs to be constructed according to method 1; when 0 < u mi <1, the virtual modulation wave u′ mi =u mi +0.1; when -1<u mi <0, the virtual modulation wave u′ mi =u mi -0.1; when u mi = 0, it remains unchanged, that is, the virtual modulation wave u′ mi =u mi ; when u mi =1, the virtual modulation wave u′ mi =u c1u +0.2; when u mi = -1, the virtual modulation wave u′ mi =u c2d -0.2. Figure 4 As shown, u′ c1 and u′ c2 is the adjusted carrier. Figure 5 As shown, u ma and u′ ma are the A-phase equivalent modulation wave and the A-phase virtual modulation wave, u mb 、u mc , u′ mb and u′ mc Same reason.

[0049] In step 5, the virtual modulation wave u′ ma , u′ mb , u′ mc With the adjusted carrier u′ c1 , u′ c2 Carrier modulation is performed to obtain an equivalent switching signal. When the equivalent modulation wave of phase A is clamped to u c1d (u c2u ), the modulation principle diagram of the virtual modulation wave and the adjusted carrier wave in one switching cycle is as follows Figure 6 shown.

[0050] By comparison Figure 6 and Figure 3 The switching signal action sequence and time obtained after the virtual modulation wave modulates the carrier wave will not change, but the correct switching signal can be reliably and effectively output at the trough and peak of the adjacent carrier wave to avoid misleading conduction, thereby greatly improving the stability of the system. Especially at high or ultra-high frequencies, the effect of improving stability is more obvious.

[0051] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A modulation wave reconstruction method based on discontinuous space vector modulation of carrier modulation, characterized in that: The method comprises the following steps: Step 1: According to the number of levels N of the multilevel converter, select N-1 stacked carriers for modulation. Let carrier u ck From top to bottom, they are u c1 ,u c2 ,u c3 ,…,u c(N-1) , where k = 1, 2, 3, ..., N-1; Step 2: According to the principle of SPWM modulation, inject the zero-sequence component to obtain the equivalent modulation wave u of discontinuous space vector modulation mi , where i = a, b, c; Step 3: Adjust the position of the carrier so that the valley value of the upper carrier among the two adjacent carriers after adjustment is greater than the peak value of the lower carrier, and the margin between the two adjacent carriers after adjustment is △x, and obtain the adjusted carrier u c ' k , where k = 1, 2, 3, ..., N-1; Step 4: Equivalent modulation wave u mi Reconstruct to form a virtual modulation wave u′ mi , where i = a, b, c; Assume that the carrier u ck The peak value is u cku , the valley value is u ckd , then the virtual modulation wave u′ mi The reconstruction method is as follows: When the number of levels N is an odd number: If u ckd <u mi <u cku , then the virtual modulation wave If u mi =u ckd , then the virtual modulation wave If u mi =u cku , then the virtual modulation wave When the number of levels N is an even number and the carrier moves up as a whole: If u ckd <u mi <u cku , then the virtual modulation wave u′ mi =u mi +(N-1-k)Δx; if umi=uckd, then the virtual modulation wave u′ mi =u mi +(N-1.5-k)Δx; if umi=ucku, then the virtual modulation wave u′ mi =u mi +(N-0.5-k)Δx; When the number of levels N is an even number and the carrier moves downward as a whole: if u ckd <u mi <u cku , then the virtual modulation wave u′ mi =u mi -(k-1)Δx; if umi=uckd, then the virtual modulation wave u′ mi =u mi -(k-1.5)Δx; if umi=ucku, then the virtual modulation wave u′ mi =u mi -(k-2.5)Δx.

2. The modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation according to claim 1 is characterized in that: In step 1, the carrier is a carrier stacked in phase or in anti-phase.

3. The modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation according to claim 1, characterized in that: In step 3, for different levels, the corresponding carrier adjustment method is as follows: Method 1: When the number of levels N is an odd number, the number of carriers is an even number, respectively The carriers above and below the middle position are each moved upward. The adjusted carrier The carriers below the center position are each moved downward The adjusted carrier Therefore, the margin between two adjacent carriers after adjustment is △x, and the adjusted carrier Method 2: When the number of levels N is an even number, the number of carriers is an odd number, except for the top carrier u c1 Or the lowest carrier u c(N-1) In addition, all carriers are moved up or down, so that the margin between two adjacent carriers after adjustment is △x.

4. The modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation according to claim 3 is characterized in that: In method 2, when uc ( N-1 ) Keep it still, when the remaining carrier moves up, the adjusted carrier u c ' k =u ck +(N-1-k)Δx; when uc1 remains unchanged and the remaining carrier moves down, the adjusted carrier u c ' k =u ck -(k-1)Δx.

5. The modulation wave reconstruction method of discontinuous space vector modulation based on carrier modulation according to claim 1, characterized in that: The method further comprises step 5, carrier modulation: the virtual modulation wave u′ obtained in step 4 is modulated mi The adjusted carrier u obtained in step 3 c ' k Carrier modulation is performed to obtain an equivalent switching signal.

Images