A single-phase multi-level flying capacitor converter and voltage balance modulation method

Abstract

The present invention relates to a single-phase multi-level flying capacitor converter and a voltage balance modulation method, which includes three pairs of switching tubes with complementary driving signals and a flying capacitor; wherein the first pair of switching tubes and the second pair of switching tubes are connected in series and then connected in parallel with the third pair of switching tubes and finally connected to the DC bus. The first pair of switching tubes and the second pair of switching tubes operate at the switching frequency, and the third pair of switching tubes operates at the fundamental frequency. The flying capacitor is connected across the second pair of switching tubes. Therefore, the present invention has the following advantages: The present invention proposes a voltage balance modulation method, which can, without changing the modulation logic, achieve different numbers of voltage level outputs by controlling the voltage of the flying capacitor at different voltage values, thereby making the topology of the single-phase multi-level flying capacitor converter more flexible and variable.

Description

Technical Field

[0001] The present invention relates to a single-phase multi-level flying capacitor converter and a voltage balance modulation method. Background Art

[0002] Compared with the traditional single-phase two-level converter, the single-phase multi-level converter can output more voltage levels, has a smaller dv / dt, smaller switching losses, and lower output harmonic content. Therefore, the volume of the required passive filter will be smaller. With the continuous pursuit of high power density and high conversion efficiency performance indicators of power converters by people, multi-level converter topologies are gradually emerging in low-voltage applications. Summary of the Invention

[0003] The above technical problems of the present invention are mainly solved by the following technical solutions:

[0004] A single-phase multi-level flying capacitor converter, characterized in that it includes three pairs of switch tubes with complementary drive signals and a flying capacitor; wherein the first pair of switch tubes and the second pair of switch tubes are connected in series and then connected in parallel with the third pair of switch tubes and finally connected to the DC bus. The first pair of switch tubes and the second pair of switch tubes operate at the switching frequency, the third pair of switch tubes operates at the fundamental frequency, and the flying capacitor is connected across the second pair of switch tubes.

[0005] In the above single-phase multi-level flying capacitor converter, each pair of switch tubes includes two series-connected switch tubes, namely the first pair of switch tubes composed of switch tube S1 and switch tube S1'; the second pair of switch tubes composed of switch tube S2 and switch tube S2'; the third pair of switch tubes composed of switch tube S3 and switch tube S3', and the flying capacitor C f is connected across switch tube S2 and switch tube S2'.

[0006] A voltage balance modulation method for a single-phase multi-level flying capacitor converter, characterized in that it receives an error signal;

[0007] The error signal is output as a drive signal through a PI regulator;

[0008] The drive signal controls the three pairs of switch tubes to balance the terminal voltage U f of the flying capacitor C Cf , so that its terminal voltage U Cf is controlled to be different ratios of the DC bus voltage U dc ;

[0009] Output different voltage levels u ab .

[0010] In the above voltage balance modulation method, if the single-phase multi-level flying capacitor converter operates in the inverter mode, the error signal ΔU ref is the flying capacitor voltage UCf The difference from the reference voltage U ref is:

[0011] ΔU Cf = U Cf - U ref

[0012] If the single-phase multi-level flying capacitor converter operates in the rectification mode, the error signal ΔU ref is the difference between the reference voltage U ref and the flying capacitor voltage U Cf :

[0013] ΔU Cf = U ref - U Cf

[0014] In the above voltage balance modulation method, it is defined that A represents the logical signal of the reference modulation signal u ref after passing through the zero-crossing comparator, and B, C, and D respectively represent the output logical signals after comparing the three modulation signals u ref1 , u ref2 , u ref3 with the carrier signal C ar . According to the truth table, the logical expressions of the driving signals of the switching tubes S1, S2, and S3 are:

[0015]

[0016] Among them, the driving signals of the switching tubes S1', S2', and S3' are complementary to the driving signals of the switching tubes S1, S2, and S3, and their logical expressions are respectively And represents the inversion of A, B, and C.

[0017] In the above voltage balance modulation method, corresponding to the three modulation signals u ref1 , u ref2 , u ref3 ;

[0018]

[0019] Among them, k is the output variable obtained by passing ΔU ref through a PI regulator.

[0020] In the above voltage balance modulation method, the different output voltage levels u ab are respectively: U dc , U dc - U Cf , U Cf , 0, - U Cf , U Cf - Udc ,-U dc .

[0021] Therefore, the present invention has the following advantages: without changing the modulation logic, the present invention can control the flying capacitor voltage at different voltage values by changing the magnitude of the reference voltage U ref , and can output different numbers of voltage levels, making the converter topology more flexible and variable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a single-phase multi-level flying capacitor converter;

[0023] Figure 2 is the voltage balance modulation strategy proposed by the present invention;

[0024] Fig. 3(a) is the equivalent circuit of the single-phase multi-level flying capacitor converter (u ab = U dc );

[0025] Fig. 3(b) is the equivalent circuit of the single-phase multi-level flying capacitor converter (u ab = U dc - U Cf );

[0026] Fig. 3(c) is the equivalent circuit of the single-phase multi-level flying capacitor converter (u ab = U Cf );

[0027] Fig. 3(d) is the equivalent circuit of the single-phase multi-level flying capacitor converter (u ab = 0);

[0028] Fig. 3(e) is the equivalent circuit of the single-phase multi-level flying capacitor converter (u ab = 0);

[0029] Fig. 3(f) is the equivalent circuit of the single-phase multi-level flying capacitor converter (u ab = - U Cf );

[0030] Fig. 3(g) is the equivalent circuit of the single-phase multi-level flying capacitor converter (u ab = U Cf – U dc );

[0031] Fig. 3(h) is the equivalent circuit of the single-phase multi-level flying capacitor converter (u ab = – U dc );

[0032] Fig. 4(a) is the Karnaugh map of the switching transistor S1;

[0033] Figure 4(b) is the Karnaugh map of switch S2;

[0034] Figure 4(c) is the Karnaugh map of switch S3;

[0035] Figure 5(a) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 1 / 2U dc (the voltage u ab before filtering, the voltage u o after filtering, and the output current i o );

[0036] Figure 5(b) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 1 / 2U dc (the flying capacitor voltage U Cf , the error signal ΔU Cf , and the output variable k of the PI regulator);

[0037] Figure 5(c) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 1 / 2U dc (the terminal voltage waveforms of each switch);

[0038] Figure 6(a) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 1 / 3U dc (the voltage u ab before filtering, the voltage u o after filtering, and the output current i o );

[0039] Figure 6(b) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 1 / 3U dc (the flying capacitor voltage U Cf , the error signal ΔU Cf , and the output variable k of the PI regulator);

[0040] Figure 6(c) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 1 / 3U dc (the terminal voltage waveforms of each switch);

[0041] Figure 7(a) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 2 / 3U dc (the voltage u ab before filtering, the voltage u o after filtering, and the output current i o );

[0042] Figure 7(b) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 2 / 3U dc (flying capacitor voltage U Cf , error signal ΔU Cf , PI regulator output variable k).

[0043] Figure 7(c) shows the simulation results of the single-phase multi-level flying capacitor converter when U Cf = 2 / 3U dc (voltage waveforms at the terminals of each switching device). Detailed implementation manners

[0044] The technical solution of the present invention will be further specifically described below through embodiments in conjunction with the accompanying drawings.

[0045] Embodiment:

[0046] As Figure 1 shown in the topology of the single-phase multi-level flying capacitor converter, it consists of three pairs of switching devices (S1, S1'), (S2, S2'), (S3, S3') with complementary drive signals and a flying capacitor C f . Among them, the switching devices (S3, S3') operate at the fundamental frequency, so their switching losses are almost zero; the switching devices (S1, S1'), (S2, S2') operate at the switching frequency. For this topology of the single-phase multi-level flying capacitor converter, the present invention proposes a voltage balance modulation strategy to balance the flying capacitor voltage. Without changing the modulation logic, by controlling the flying capacitor voltage at different voltage values, different numbers of voltage levels can be output, making the converter topology more flexible and variable.

[0047] To ensure the normal operation of the single-phase multi-level flying capacitor converter, it is necessary to balance the terminal voltage U f of the flying capacitor C Cf . To achieve this goal, the present invention proposes a voltage balance modulation strategy as Figure 2 shown, in which the magnitude of the reference modulation signal u ref is:

[0048] u ref = 2msin(2πf m t) (1)

[0049] where m is the modulation ratio and f m is the fundamental frequency.

[0050] In the voltage balance modulation strategy as Figure 2 shown, if the single-phase multi-level flying capacitor converter operates in the inverter mode, the flying capacitor voltage U Cf and the reference voltage U refSubtract to obtain the error signal ΔU ref , as shown in (2).

[0051] ΔU Cf = U Cf - U ref (2)

[0052] If the single-phase multi-level flying capacitor converter operates in the rectification mode, the flying capacitor voltage U ref is subtracted from the reference voltage U Cf to obtain the error signal ΔU ref , as shown in (3).

[0053] ΔU Cf = U ref - U Cf (3)

[0054] ΔU ref Passes through a PI regulator to obtain the output variable k. Combining with formula (1), the reference modulation signal u ref can be further evolved into three modulation signals u ref1 , u ref2 , u ref3 , as shown in formula (4).

[0055]

[0056] According to the equivalent circuit of the single-phase multi-level flying capacitor converter shown in Figure 3, the truth table of the single-phase multi-level flying capacitor converter shown in Table 1 can be established. In Table 1, A represents the logic signal after the reference modulation signal u ref passes through the zero-crossing comparator, and B, C, and D respectively represent the output logic signals after the three modulation signals u ref1 , u ref2 , u ref3 are compared with the carrier signal C ar . In addition, X in Table 1 can be a logical value of 1 or 0.

[0057] Table 1. Truth Table of Single-Phase Multi-Level Flying Capacitor Converter

[0058]

[0059] According to the truth table, the Karnaugh map of the single-phase multi-level flying capacitor converter can be further established, as shown in Figure 4. According to this Karnaugh map, it is not difficult to deduce the logical expressions of the drive signals of the switching tubes S1, S2, and S3 as follows:

[0060]

[0061] Among them, the switching transistors S1', S2', S3' are complementary to the switching transistors S1, S2, S3, and their logical expressions are respectively And Indicates that A, B, and C are inverted.

[0062] Based on the proposed voltage balance modulation strategy, the output voltage u of this single-phase multilevel flying capacitor converter ab Has the following voltage levels: U dc , U dc -U Cf , U Cf , 0, -U Cf , U Cf -U dc , -U dc . According to the different magnitudes of the flying capacitor voltage U Cf , different numbers of voltage levels can be output by this single-phase multilevel flying capacitor converter.

[0063] 1) When the flying capacitor voltage U Cf Is controlled to be half of the DC bus voltage U dc (i.e., 1 / 2U dc ), the output voltage u of this single-phase multilevel flying capacitor converter ab Has 5 voltage levels: U dc , 1 / 2U dc , 0, -1 / 2U dc , -U dc .

[0064] 2) When the flying capacitor voltage U Cf Is controlled to be one-third of the DC bus voltage U dc (i.e., 1 / 3U dc ), or U Cf Is controlled to be two-thirds of the DC bus voltage U dc (i.e., 2 / 3U dc ), the output voltage u of this single-phase multilevel flying capacitor converter ab Both have 7 voltage levels: U dc , 2 / 3U dc , 1 / 3U dc , 0, -1 / 3U dc , -2 / 3U dc , -U dc .

[0065] To demonstrate the feasibility of the proposed voltage balance modulation strategy, a 6.6 kW simulation model is initially established in this project, and the specific simulation parameters are shown in Table 2.

[0066] Table 2. Simulation Parameters of Single-Phase Multilevel Flying Capacitor Converter

[0067]

[0068] 1) When the flying capacitor reference voltage U ref = 1 / 2U dc , the simulation results of the single-phase multi-level flying capacitor converter are shown in Figure 5. It is not difficult to see that the flying capacitor voltage U Cf successfully stabilizes at half of the DC bus voltage, that is, 200V. The output variable k of the PI regulator successfully stabilizes near 2. The output voltage u ab of the single-phase multi-level flying capacitor converter presents a five-level output waveform, namely U dc , 1 / 2U dc , 0, -1 / 2U dc , -U dc .

[0069] 2) When the flying capacitor reference voltage U ref = 1 / 3U dc , the simulation results of the single-phase multi-level flying capacitor converter are shown in Figure 6. It is not difficult to see that the flying capacitor voltage U Cf successfully stabilizes at one-third of the DC bus voltage, that is, 133.3V. The output variable k of the PI regulator successfully stabilizes near 2. The output voltage u ab of the single-phase multi-level flying capacitor converter presents a seven-level output waveform, namely U dc , 2 / 3U dc , 1 / 3U dc , 0, -1 / 3U dc , -2 / 3U dc , -U dc .

[0070] 3) When the flying capacitor reference voltage U ref = 2 / 3U dc , the simulation results of the single-phase multi-level flying capacitor converter are shown in Figure 7. It is not difficult to see that the flying capacitor voltage U Cf successfully stabilizes at two-thirds of the DC bus voltage, that is, 266.6V. The output variable k of the PI regulator successfully stabilizes near 2. The output voltage u ab of the single-phase multi-level flying capacitor converter presents a seven-level output waveform, namely U dc , 2 / 3U dc , 1 / 3U dc , 0, -1 / 3U dc , -2 / 3U dc , -U dc .

[0071] The specific embodiments described in this invention are only illustrative of the spirit of this invention. Those skilled in the art to which this invention pertains can make various modifications or supplements to the described specific embodiments or use similar means for substitution, but they will not deviate from the spirit of this invention or exceed the scope defined by the appended claims.

Claims

1. A single-phase multi-level flying capacitor converter, characterized in that, It includes three pairs of switching tubes with complementary driving signals and a flying capacitor; among them, the first pair of switching tubes and the second pair of switching tubes are connected in series and then in parallel with the third pair of switching tubes and finally connected to the DC bus. The first pair of switching tubes and the second pair of switching tubes operate at the switching frequency, the third pair of switching tubes operates at the fundamental frequency, and the flying capacitor is connected across the second pair of switching tubes; The voltage balance modulation method of the single-phase multilevel flying capacitor converter includes: Receiving an error signal; The error signal is output as a driving signal through a PI regulator; The driving signal controls the terminal voltage U of three pairs of switching tubes to balance the flying capacitor C f such that its terminal voltage U Cf is controlled to different ratios of the DC bus voltage U Cf ; dc ​ Output different voltage levels u ab ; Define A as the reference modulation signal u ref The logic signal after passing through the zero-crossing comparator. B, C, and D respectively represent three modulation signals u ref1 , u ref2 , u ref3 And the output logic signals after comparing with the carrier signal C ar According to the truth table, the logic expressions of the driving signals of the switching transistors S1, S2, and S3 are as follows: Among them, the driving signals of the switching transistors S1', S2', and S3' are complementary to the driving signals of the switching transistors S1, S2, and S3, and their logical expressions are respectively And Indicates that A, B, and C are inverted; Each pair of switching tubes includes two series-connected switching tubes, namely, the first pair of switching tubes composed of switching tube S1 and switching tube S1'; the second pair of switching tubes composed of switching tube S2 and switching tube S2'; the third pair of switching tubes composed of switching tube S3 and switching tube S3', and the flying capacitor C f is connected across switching tube S2 and switching tube S2'; Corresponding to three modulation signals u ref1 、u ref2 、u ref3 ; where k is the error signal ΔU ref and is the output variable obtained through a PI regulator.

2. The single-phase multilevel flying capacitor converter according to claim 1, characterized in that, If the single-phase multilevel flying capacitor converter operates in the inverter mode, the error signal ΔU ref is the difference between the flying capacitor voltage U Cf and the reference voltage U ref : ΔU ref = U Cf - U ref If the single-phase multilevel flying capacitor converter operates in the rectification mode, the error signal ΔU ref is the difference between the reference voltage U ref and the flying capacitor voltage U Cf : ΔU ref = U ref - U Cf .

3. The single-phase multi-level flying capacitor converter according to claim 1, wherein The different output voltage levels u ab are respectively: U dc , U dc , -U Cf , U Cf , 0, -U Cf , U Cf , -U dc , -U dc .

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