Transformation system

Abstract

The present invention provides a conversion system, comprising a conversion circuit and a filtering circuit. The filtering circuit includes a first inductor, a second inductor, a first notch filter, and a resonant filtering branch. A first end of the first inductor is coupled to a first end of the filtering circuit. The second inductor is coupled between a second end of the first inductor and a second end of the filtering circuit. A first end of the first notch filter is coupled to the second end of the first inductor and a first end of the second inductor. A second end of the first notch filter is coupled to the second end of the second inductor and the second end of the filtering circuit via an internal X capacitor. The first notch filter includes a third inductor and a capacitor connected in series. A first end of the resonant filtering branch is coupled between the second end of the first inductor and the second end of the filtering circuit. The resonant filtering branch includes a capacitor component and a fourth inductor connected in series.

Description

Technical Field

[0001] The present invention relates to a conversion system, and particularly to a conversion system that suppresses resonance, reduces volume and saves costs. Background Art

[0002] In the traditional power field, a conversion system is used to convert DC electrical energy and AC electrical energy into each other. Figure 1 FIG. is a schematic circuit diagram of a first traditional conversion system. Figure 2 For Figure 1 FIG. shows the frequency-gain Bode plot of the bridge arm voltage to the internal X-capacitor current of the traditional conversion system shown. As Figure 1 and Figure 2 shown, during the process of converting electrical energy by the traditional conversion system 1', at the switching frequency of the traditional conversion system 1' (such as Figure 2 15 kHz shown) and at twice the switching frequency (such as Figure 2 30 kHz shown), resonance is likely to occur and form resonance points, causing resonance between the power grid and the traditional converter system 1'. When the current generated by this resonance is too large, the components in the traditional conversion system 1' will be damaged due to overcurrent. Figure 3 For Figure 1 FIG. shows the waveform diagram of the current of the key branch inside the external X-capacitor-module of the traditional conversion system 1' shown. As Figure 3 shown, when the external leakage inductance Lt of the traditional conversion system 1' is fixed (for example, 180 μH), as the external X-capacitor Cx_out changes, the current flowing through the switching frequency sub-notch filter T1 (15K Notch Filter) and the twice switching frequency notch filter T2 (30K Notch Filter) inside the traditional conversion system 1' changes with the change of the external X-capacitor Cx_out. When the external X-capacitor Cx_out is near a certain value, the current value will be too large, making the components constituting the notch filter T1 and the notch filter T2 likely to be damaged due to overcurrent. The traditional conversion system 1' avoids the resonance point composed of the changes of the external X-capacitor Cx_out and the leakage inductance Lt by greatly increasing the capacitance value of the internal X-capacitor Cx_in, but this method is not conducive to controlling the cost and volume of the conversion system 1'.

[0003] Therefore, there is an urgent need to develop a conversion system that can improve the above-mentioned existing technologies. Summary of the Invention

[0004] The object of the present invention is to provide a conversion system that can suppress resonance, reduce volume and save costs.

[0005] To achieve the above object, the present invention provides a conversion system, electrically coupled to the power grid, and the conversion system has a switching frequency. The conversion system includes a conversion circuit and a filtering circuit. The conversion circuit is used for AC-DC conversion. The filtering circuit has a first end and a second end. The first end of the filtering circuit is electrically coupled to the conversion circuit, and the second end of the filtering circuit is electrically coupled to the power grid. The filtering circuit filters the AC electrical energy. The filtering circuit includes a first inductor, a second inductor, a first notch filter, and a first resonant filtering branch. The first inductor has a first end and a second end, and the first end of the first inductor is electrically coupled to the first end of the filtering circuit. The second inductor has a first end and a second end, the first end of the second inductor is electrically coupled to the second end of the first inductor, and the second end of the second inductor is electrically coupled to the second end of the filtering circuit. The first notch filter has a first end and a second end, the first end of the first notch filter is electrically coupled to the second end of the first inductor and the first end of the second inductor, and the second end of the first notch filter is electrically coupled to the second end of the second inductor and the second end of the filtering circuit via an internal X capacitor, and the first notch filter includes a third inductor and a first capacitor connected in series. The first resonant filtering branch has a first end and a second end, the first end of the first resonant filtering branch is electrically coupled to the second end of the first inductor and the first end of the second inductor, and the second end of the first resonant filtering branch is electrically coupled to the second end of the second inductor and the second end of the filtering circuit, and the first resonant filtering branch includes a first capacitor component and a fourth inductor connected in series. Description of the Drawings

[0006] Figure 1 It is a schematic circuit diagram of a first conventional conversion system.

[0007] Figure 2 For Figure 1 The frequency-gain Bode plot of the bridge arm voltage to the internal X capacitor current of the conventional conversion system shown.

[0008] Figure 3 For Figure 1 The waveform diagram of the external X capacitor - key branch current inside the module of the conventional conversion system shown.

[0009] Figure 4 It is a schematic circuit diagram of the conversion system according to the first preferred embodiment of the present invention.

[0010] Figure 5 It is a schematic circuit diagram of a second conventional conversion system.

[0011] Figure 6 For Figure 4 The conversion system shown and Figure 5 The frequency-gain Bode comparison plot of the bridge arm voltage to the grid-connected current of the conventional conversion system shown.

[0012] Figure 7 For Figure 4Waveform diagram of the current in the key branch inside the module of the external X capacitance of the transformation system shown

[0013] Figure 8 Schematic circuit diagram of the transformation system of the second preferred embodiment of the present invention

[0014] Figure 9A For Figure 8 Comparison diagram of the influence of the error of the fourth inductance component of the first resonant filtering branch of the transformation system shown and the frequency gain Bode plot of the traditional transformation system

[0015] Figure 9B For Figure 8 Comparison diagram of the influence of the error of the first capacitance component of the first resonant filtering branch of the transformation system shown and the frequency gain Bode plot of the traditional transformation system

[0016] Figure 10 Schematic circuit diagram of the transformation system of the third preferred embodiment of the present invention

[0017] Figure 11 For Figure 10 Comparison diagram of the frequency - gain Bode plot from the arm voltage to the grid - connected current of the transformation system shown and the traditional transformation system

[0018] Figure 12 For Figure 10 Waveform diagram of the current in the key branch inside the module of the external X capacitance of the transformation system shown

[0019] Figure 13 Schematic circuit diagram of the transformation system of the fourth preferred embodiment of the present invention

[0020] Among them, the reference numerals are explained as follows:

[0021] 1’: Traditional transformation system

[0022] T1, T2: Notch filters

[0023] Lt: External leakage inductance

[0024] Cx_out: External X capacitance

[0025] 1, 1a, 1b, 1c: Transformation systems

[0026] 2: Power grid

[0027] Cx_in: Internal X capacitance

[0028] 3: Conversion circuit

[0029] 4: Filter circuit

[0030] 41: First terminal

[0031] 42: Second terminal

[0032] Linv: First inductor

[0033] 51: First terminal

[0034] 52: Second terminal

[0035] Lg1: Second inductor

[0036] 53: First terminal

[0037] 54: Second terminal

[0038] 43: First notch filter

[0039] 431: First terminal

[0040] 432: Second terminal

[0041] Ln1: Third inductor

[0042] Cn1: First capacitor

[0043] 44: First resonant filter branch

[0044] 441: First terminal

[0045] 442: Second terminal

[0046] 443: First capacitor component

[0047] Cr1: Second capacitor

[0048] Cn1_r: Third capacitor

[0049] Ln1_r: Fourth inductor

[0050] 45: Damping branch

[0051] 451: First terminal

[0052] 452: Second terminal

[0053] Rd: Damping resistor

[0054] Cd: Damping capacitor

[0055] Cg1: Capacitor

[0056] 46: Second notch filter

[0057] 461: First terminal

[0058] 462: Second terminal

[0059] Ln2: Fifth inductor

[0060] Cn2: Fourth capacitor

[0061] Lg2: The sixth inductor

[0062] 55: The first terminal

[0063] 56: The second terminal

[0064] 47: The second resonant filter branch

[0065] 471: The first terminal

[0066] 472: The second terminal

[0067] 473: The second capacitor component

[0068] Cr2: The fifth capacitor

[0069] Cn2_r: The sixth capacitor

[0070] Ln2_r: The seventh inductor

[0071] N: The common connection point Detailed implementation manners

[0072] Some typical embodiments embodying the features and advantages of the present disclosure will be described in detail in the following description. It should be understood that the present disclosure can have various variations in different implementation manners, all of which do not depart from the scope of the present disclosure, and the descriptions and illustrations therein are essentially for illustrative purposes and not for limiting the present disclosure.

[0073] Please refer to Figure 4 , which is a schematic circuit diagram of the conversion system of the first preferred embodiment of the present invention. As Figure 4 shown, the conversion system 1 can be applied to an electronic load, an active power filter, a static var generator, a bidirectional converter, a rectifier, a photovoltaic converter, or an uninterruptible power supply system, etc., and is electrically coupled to the power grid 2 via an external leakage inductance Lt and an external X capacitor Cx_out, wherein the conversion system 1 is connected in series with the external leakage inductance Lt and in parallel with the external X capacitor Cx_out and is electrically coupled to the power grid 2. The conversion system 1 has a switching frequency, for example but not limited to 15 kHz, and the conversion system 1 includes a conversion circuit 3 and a filter circuit 4. The conversion circuit 3 is used for AC-DC conversion. The filter circuit 4 has a first terminal 41 and a second terminal 42. The first terminal 41 of the filter circuit 4 is electrically coupled to the conversion circuit 3, and the second terminal 42 of the filter circuit 4 is electrically coupled to the power grid 2 via the external leakage inductance Lt. The filter circuit 4 is used for filtering the alternating current and includes a first inductor Linv, a second inductor Lg1, a first notch filter 43, a first resonant filter branch 44, and an internal X capacitor Cx_in.

[0074] The first inductor Linv has a first terminal 51 and a second terminal 52. The first terminal 51 of the first inductor Linv is electrically coupled to the first terminal 41 of the filter circuit 4. The second inductor Lg1 has a first terminal 53 and a second terminal 54. The first terminal 53 of the second inductor Lg1 is electrically coupled to the second terminal 52 of the first inductor Linv. The second terminal 54 of the second inductor Lg1 is electrically coupled to the second terminal 42 of the filter circuit 4. Since the second terminal 42 of the filter circuit 4 is electrically coupled to the power grid 2, the second inductor Lg1 forms the grid-side inductor of the conversion system 1. The first notch filter 43 has a first terminal 431 and a second terminal 432. The first terminal 431 of the first notch filter 43 is electrically coupled to the second terminal 52 of the first inductor Linv and the first terminal 53 of the second inductor Lg1. The second terminal 432 of the first notch filter 43 is electrically coupled to a common connection point N, where the common connection point N can be but is not limited to a ground terminal. And the first notch filter 43 includes a third inductor Ln1 and a first capacitor Cn1 connected in series. One end of the third inductor Ln1 is electrically coupled to the first terminal 431 of the first notch filter 43. The other end of the third inductor Ln1 is electrically coupled to one end of the first capacitor Cn1. The other end of the first capacitor Cn1 is electrically coupled to the second terminal 432 of the first notch filter 43. One end of the internal X capacitor Cx_in is electrically coupled to the second terminal 54 of the second inductor Lg1 and the second terminal 42 of the filter circuit 4. The other end of the internal X capacitor Cx_in is electrically coupled to the common connection point N. And the second terminal 432 of the first notch filter 43 is electrically coupled to the second terminal 54 of the second inductor Lg1 and the second terminal 42 of the filter circuit 4 through the internal X capacitor Cx_in.

[0075] The first resonant filter branch 44 is connected in parallel with the second inductor Lg1 and has a first terminal 441 and a second terminal 442. The first terminal 441 of the first resonant filter branch 44 is electrically coupled to the second terminal 52 of the first inductor Linv, the first terminal 53 of the second inductor Lg1, and the first terminal 431 of the first notch filter 43. The second terminal 442 of the first resonant filter branch 44 is electrically coupled to the second terminal 54 of the second inductor Lg1 and the second terminal 42 of the filter circuit 4. And the first resonant filter branch 44 includes a first capacitor component 443 and a fourth inductor Ln1_r connected in series. One end of the first capacitor component 443 is electrically coupled to the first terminal 441 of the first resonant filter branch 44. The other end of the first capacitor component 443 is electrically coupled to one end of the fourth inductor Ln1_r. The other end of the fourth inductor Ln1_r is electrically coupled to the second terminal 442 of the first resonant filter branch 44. In this embodiment, the first capacitor component 443 includes a second capacitor Cr1 and a third capacitor Cn1_r connected in series. One end of the second capacitor Cr1 is electrically coupled to the first terminal 441 of the first resonant filter branch 44. The other end of the second capacitor Cr1 is electrically coupled to one end of the third capacitor Cn1_r. The other end of the third capacitor Cn1_r is electrically coupled to the fourth inductor Ln1_r.

[0076] In this embodiment, the components in the conversion system 1 are exemplified by the following values. Of course, this is not limiting, and components with different value specifications can be selected according to different requirements. Among them, the second inductor Lg1 is 20 μH, the second capacitor Cr1 is 5.6 μF, the third capacitor Cn1_r is 1 μF, the external leakage inductance Lt is 180 μH, the internal X capacitor Cx_in is 1.4 μF, the external X capacitor Cx_out is 2 μF, and the fourth inductor Ln1_r is 112.6 μH.

[0077] Please refer to Figure 5 and Figure 6 and cooperate with Figure 4 , where Figure 5 is a schematic circuit diagram of a second traditional conversion system, Figure 6 is Figure 4 the frequency-gain Bode comparison diagram of the bridge arm voltage to the grid-connected current of the conversion system shown and Figure 5 the traditional conversion system shown. Figure 6 The solid line in Figure 5 represents the frequency-gain Bode plot of the traditional conversion system shown in Figure 6 , and the dashed line in Figure 4 represents the frequency-gain Bode plot of the conversion system 1 of the present invention shown in Figure 4 and Figure 6 It can be known that the third inductor Ln1 and the first capacitor Cn1 of the first notch filter 43 can jointly generate a first notch impedance, and the first notch impedance generated by the third inductor Ln1 and the first capacitor Cn1 of the first notch filter 43 at the switching frequency (15 kHz) is 0, and the third inductor Ln1 and the first capacitor Cn1 satisfy the following switching frequency formula,

[0078]

[0079] where f sw represents the switching frequency, Ln1 represents the inductance of the third inductor, and Cn1 represents the capacitance value of the first capacitor. In addition, the second capacitor Cr1 in the first capacitor assembly 443 of the first resonant filter branch 44 of the conversion system 1 in this embodiment and the second inductor Lg1 form a switching frequency sub-parallel impedance, and jointly generate a first impedance (i.e., the switching frequency sub-parallel impedance). Among them, the first impedance generated by the second capacitor Cr1 and the second inductor Lg1 at the switching frequency (15 kHz) is infinite, and the second capacitor Cr1 and the second inductor Lg1 satisfy the following switching frequency formula,

[0080]

[0081] where f swf represents the switching frequency, Lg1 represents the inductance of the second inductor, and Cr1 represents the capacitance value of the second capacitor. Thus, the gain of the conversion system 1 in this embodiment at the switching frequency is relatively low, and thus it can more effectively prevent the current ripple excitation generated by the conversion system 1 at the switching frequency from being transmitted to the power grid 2, and from Figure 6 As can be clearly seen from the detailed enlarged Bode plot on the right side in, the gain of the conversion system 1 in this embodiment at the switching frequency is -57.2 dB, while the gain of a traditional conversion system with the same filter circuit parameters and without the first resonant filter branch 44 at the switching frequency is -35.9 dB. Therefore, it can be known that the gain of the conversion system 1 in this embodiment at the switching frequency is 21.3 dB smaller than the gain of the traditional conversion system at the switching frequency. Therefore, the filtering ability of the conversion system 1 in this embodiment at the switching frequency is stronger than that of the traditional conversion system at the switching frequency. Further, a sub-series impedance at the switching frequency is formed between the third capacitor Cn1_r and the fourth inductor Ln1_r in the first capacitor component 443 of the first resonant filter branch 44, and a second impedance (i.e., the sub-series impedance at the switching frequency) is jointly generated, wherein the second impedance generated by the third capacitor Cn1_r and the fourth inductor Ln1_r at the switching frequency is 0, and the third capacitor Cn1_r and the fourth inductor Ln1_r satisfy the following switching frequency formula,

[0082]

[0083] where f sw represents the switching frequency, Ln1_r represents the inductance of the fourth inductor, and Cn1_r represents the capacitance value of the third capacitor. Thus, the phenomenon that the attenuation of the high-frequency part becomes worse due to the increase in the sub-parallel resonant impedance at the switching frequency in this embodiment can be improved, so that the conversion system 1 in this embodiment has the same filtering effect as the traditional converter system 1' at high frequencies, and reference can be made to Figure 6 The curves of the two coincide in the high-frequency part from 3×10 6 -1×10 8 Hz, and thus have the same suppression effect on EMI, reducing the problems caused by EMI.

[0084] In some embodiments, the filtering circuit 4 of the conversion system 1 further includes a damping branch 45. The damping branch 45 is connected in parallel with the first notch filter 43 and has a first end 451 and a second end 452. The first end 451 of the damping branch 45 is electrically coupled to the second end 52 of the first inductor Linv, the first end 53 of the second inductor Lg1, the first end 431 of the first notch filter 43, and the first end 441 of the first resonant filtering branch 44. The second end 452 of the damping branch 45 is electrically coupled to the second end 432 of the first notch filter 43 and the common connection point N. And the damping branch 45 includes a damping resistor Rd and a damping capacitor Cd connected in series. One end of the damping resistor Rd is electrically coupled to the first end 451 of the damping branch 45. The other end of the damping branch 45 is electrically coupled to one end of the damping capacitor Cd. The other end of the damping capacitor Cd is electrically coupled to the second end 452 of the damping branch 45.

[0085] Please refer to Figure 7 and cooperate with Figure 4 , where Figure 7 is Figure 4 the waveform diagram of the current of the external X-capacitor - the key branch inside the module of the conversion system shown. Figure 7 It shows the waveform relationship between the current flowing into the first notch filter 43, the resonant current of the second inductor Lg1, and the current of the internal X-capacitor Cx_in and the external X-capacitor Cx_out when the conversion system 1 operates at the switching frequency (15 kHz). As Figure 7 shown, when the external leakage inductance Lt of the conversion system 1 in this embodiment is fixed, the currents flowing into the first notch filter 43, the resonant current of the second inductor Lg1, and the current of the internal X-capacitor Cx_in do not increase due to the increase in the capacitance value of the external X-capacitor Cx_out. Therefore, it can be known that the currents flowing into the first notch filter 43, the first resonant filtering branch 44, the second inductor Lg1, and the internal X-capacitor Cx_in of the conversion system 1 of the present invention are all very stable and are not easily affected by changes in external parameters. Therefore, the conversion system 1 of the present invention is not affected by the change in the capacitance value of the external X-capacitor Cx_out to generate resonance and has a better ability to suppress resonance caused by changes in external parameters, and the reliability of the conversion system is significantly improved. In addition, from Figure 7 it can be seen that the resonant current value flowing into the second inductor Lg1 is almost fixed at 6 Arms. Since the current value is very stable, the capacitance values of the second capacitor Cr1 and the third capacitor Cn1_r and the inductance value of the fourth inductor Ln1_r in the first resonant filtering branch 44 are also easier to select and design.

[0086] And according to the above conclusion, the components in the conversion system 1 of the present invention can select components with lower current specifications compared to the traditional conversion system 1'. For example, Figure 1For the inductor with an inductance of 54.4 μH in the 15KHz notch filter of the traditional conversion system 1', an inductor with a current rating of at least 45A must be selected. However, for the third inductor Ln1 of the first notch filter 43 of the conversion system 1 of the present invention, an inductor with the same inductance but a current rating of only 19A can be selected; Figure 1 For the capacitor with a capacitance of 2.4 μF in the notch filter of the traditional conversion system 1', a capacitor with a current rating of at least 45A must be selected. However, for the first capacitor Cn1 of the first notch filter 43 of the conversion system 1 of the present invention, a capacitor with the same capacitance as the traditional conversion system 1' but a current rating of only 19A can be selected; Figure 1 For the capacitor with a capacitance of 1.2 μF of Cx_in in the traditional conversion system 1', a capacitor with a current rating of at least 12A must be selected. However, for the internal X capacitor Cx_in of the conversion system 1 of the present invention, a capacitor with the same capacitance but a current rating of only 2A can be selected; Figure 1 When selecting the line-side inductor with an inductance of 20 μH in the traditional conversion system 1', in addition to meeting the rated current for normal operation, a margin of 35A resonance current due to resonance needs to be additionally considered. However, for the second inductor Lg1 used to form the line-side inductor of the conversion system 1 of the present invention, an inductor with the same inductance as the traditional conversion system 1' can be selected, but the additional resonance current margin to be considered is only 7.5A. In summary, the wire diameter of the line-side inductor of the conversion system of the present invention can be reduced, and the cost and volume can be further reduced. Additionally, for the second capacitor Cr1 in the conversion system 1 of the present invention, a capacitor with a current rating of only 7.5A and a capacitance of 5.6 μF can be selected, for the third capacitor Cn1_r, a capacitor with a current rating of only 7.5A and an inductance of 1 μF can be selected, and for the fourth inductor Ln1_r, an inductor with a current rating of only 7.5A and an inductance of 112.6 μH can be selected. Therefore, it can be seen that the current ratings of the components in the conversion system 1 of the present invention are not only lower than those of the components in the traditional conversion system 1', and the additional second capacitor Cr1, third capacitor Cn1_r, and fourth inductor Ln1_r in the conversion system 1 can also select capacitors and inductors with low current ratings. Therefore, the conversion system 1 of the present invention can achieve the effects of reducing volume and saving costs.

[0087] In some embodiments, the second capacitor Cr1 and the third capacitor Cn1_r can be combined into a single capacitor Cg1, that is, the first capacitor assembly 443 can be composed of the single capacitor Cg1. Please refer to Figure 8 which is the circuit structure schematic diagram of the conversion system of the second preferred embodiment of the present invention. As Figure 8 shown, the conversion system 1a of this embodiment is similar to Figure 4The transformation system 1 shown is not described again. In this embodiment, the components in the transformation system 1a are exemplified by the following values. Of course, this is not limited thereto, and components with different value specifications can be selected according to different requirements. Among them, the second inductor Lg1 is 20 μH, the first capacitor assembly 443 is 0.85 μF, the external leakage inductance Lt is 180 μH, the internal X capacitor Cx_in is 1.4 μF, the external X capacitor Cx_out is 2 μF, and the fourth inductor Ln1_r is 112.6 μH.

[0088] In practical applications, there may be errors in the inductance of the fourth inductor Ln1_r of the first resonant filter branch 44 and the capacitance value of the first capacitor assembly 443. The following will illustrate the impact of component errors on the transformation system 1. Please refer to Figure 9A and cooperate with Figure 8 where Figure 9A is Figure 8 the comparison diagram of the frequency gain of the bridge arm voltage to grid-connected current of the fourth inductor component error of the first resonant filter branch of the transformation system shown and that of the traditional transformation system. Figure 9A respectively show the frequency-gain comparison diagrams of the transformation system 1 of the present invention with no error in the inductance of the fourth inductor Ln1_r, the transformation system 1 of the present invention with a +10% error in the inductance of the fourth inductor Ln1_r, the transformation system 1 of the present invention with a -10% error in the inductance of the fourth inductor Ln1_r, and the traditional transformation system 1' with no error. When there is no error in the inductance of the fourth inductor Ln1_r of the transformation system 1 of the present invention, the gain of the transformation system 1 at the switching frequency (15 kHz) is -57.2 dB; when there is a +10% error in the inductance of the fourth inductor Ln1_r of the transformation system 1 of the present invention, the gain of the transformation system 1 at the switching frequency (15 kHz) is -46.9 dB; when there is a -10% error in the inductance of the fourth inductor Ln1_r of the transformation system 1 of the present invention, the gain of the transformation system 1 at the switching frequency (15 kHz) is -41.5 dB. However, the gain of the traditional transformation system at the switching frequency is -35.9 dB. Therefore, it can be seen that although there is a +10% or -10% error in the inductance of the fourth inductor Ln1_r of the transformation system 1 of the present invention, the gain of the transformation system 1 of the present invention at the switching frequency is still smaller than that of the traditional transformation system 1' at the switching frequency. Therefore, when there is a +10% or -10% error in the inductance of the fourth inductor Ln1_r of the transformation system 1 of the present invention, the filtering ability of the transformation system 1 of the present invention is still stronger than that of the traditional transformation system 1'. As can be seen from the above, the inductance of the fourth inductor Ln1_r of the transformation system 1 of the present invention can allow an error of at least ±10%.

[0089] Please refer to Figure 9B and cooperate with Figure 8 whereFigure 9B For Figure 8 The first capacitance component component error influence of the first resonant filtering branch of the transformation system shown and the frequency gain Bode plot comparison of the traditional transformation system. Figure 9B It respectively shows the frequency-gain comparison diagrams of the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention without error, the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention having a +5% error, the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention having a -5% error, and the traditional transformation system 1' without error. When the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention has no error, the gain of the transformation system 1 at the switching frequency (15 kHz) is -57.2 dB; when the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention has a +5% error, the gain of the transformation system 1 at the switching frequency (15 kHz) is -56.9 dB; when the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention has a -5% error, the gain of the transformation system 1 at the switching frequency (15 kHz) is -56.3 dB. However, the gain of the traditional transformation system 1' at the switching frequency is -35.9 dB. Therefore, it can be seen that although the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention has a +5% or -5% error, the gain of the transformation system 1 of the present invention at the switching frequency is still smaller than the gain of the traditional transformation system 1' at the switching frequency. Therefore, when the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention has a +5% or -5% error, the filtering ability of the transformation system 1 of the present invention is still stronger than that of the traditional transformation system 1'. From the above, it can be seen that the capacitance value of the first capacitance component 443 of the transformation system 1 of the present invention can allow an error of at least ±5%.

[0090] Please refer to Figure 10 , which is a schematic circuit structure diagram of the transformation system of the third preferred embodiment of the present invention. The transformation system 1b of this embodiment is similar to Figure 4The transformation system 1 shown. However, in this embodiment, the filter circuit 4 of the transformation system 1b further includes a second notch filter 46. The second notch filter 46 is connected in parallel with the first notch filter 43 and the damping branch 45. The second notch filter 46 has a first end 461 and a second end 462. The first end 461 of the second notch filter 46 is electrically coupled to the second end 52 of the first inductor Linv, the first end 53 of the second inductor Lg1, the first end 431 of the first notch filter 43, and the first end 451 of the damping branch 45. The second end 462 of the second notch filter 46 is electrically coupled to the second end 432 of the first notch filter 43, the second end 452 of the damping branch 45, and the common connection end N. The second notch filter 46 includes a fifth inductor Ln2 and a fourth capacitor Cn2 connected in series. One end of the fifth inductor Ln2 is electrically coupled to the first end 461 of the second notch filter 46, the other end of the fifth inductor Ln2 is electrically coupled to one end of the fourth capacitor Cn2, and the other end of the fourth capacitor Cn2 is electrically coupled to the second end 462 of the second notch filter 46.

[0091] In addition, in this embodiment, the filter circuit 4 of the transformation system 1b of this embodiment, in addition to including the second inductor Lg1 and the first resonant filter branch 44, further includes a sixth inductor Lg2 and a second resonant filter branch 47. The sixth inductor Lg2 has a first end 55 and a second end 56. The first end 55 of the sixth inductor Lg2 is electrically coupled to the second end 54 of the second inductor Lg1, and the second end 56 of the sixth inductor Lg2 is electrically coupled to the second end 42 of the filter circuit 4. The sixth inductor Lg2 and the second inductor Lg1 are connected in series between the second end 52 of the first inductor Linv and the second end 42 of the filter circuit 4. The second resonant filter branch 47 is connected in parallel with the sixth inductor Lg2 and has a first end 471 and a second end 472. The first end 471 of the second resonant filter branch 47 is electrically coupled to the second end 54 of the second inductor Lg1 and the first end 55 of the sixth inductor Lg2, and the second end 472 of the second resonant filter branch 47 is electrically coupled to the second end 56 of the sixth inductor Lg2 and the second end 42 of the filter circuit 4. The second resonant filter branch 47 includes a second capacitor component 473 and a seventh inductor Ln2_r connected in series. One end of the second capacitor component 473 is electrically coupled to the first end 471 of the second resonant filter branch 47, the other end of the second capacitor component 473 is electrically coupled to one end of the seventh inductor Ln2_r, and the other end of the seventh inductor Ln2_r is electrically coupled to the second end 472 of the second resonant filter branch 47.

[0092] In this embodiment, the second capacitor component 473 includes a fifth capacitor Cr2 and a sixth capacitor Cn2_r connected in series. One end of the fifth capacitor Cr2 is electrically connected to the first end 471 of the second resonant filter branch 47, the other end of the fifth capacitor Cr2 is electrically connected to one end of the sixth capacitor Cn2_r, and the other end of the sixth capacitor Cn2_r is electrically connected to the second end 472 of the second resonant filter branch 47.

[0093] Please refer to Figure 11 and in conjunction with Figure 10 , where Figure 11 is Figure 10 the frequency-gain Bode comparison diagram of the transformation system shown and the traditional transformation system. Figure 11 The solid line in Figure 1 represents the frequency-gain Bode diagram of the traditional transformation system as shown in Figure 11 , and the dashed line in Figure 10 represents the frequency-gain Bode diagram of the transformation system 1b of the present invention as shown in Figure 10 and Figure 11 It can be known that the fifth inductor Ln2 and the fourth capacitor Cn2 of the second notch filter 46 can jointly generate a second notch impedance, and the second notch impedance generated by the fifth inductor Ln2 and the fourth capacitor Cn2 of the second notch filter 46 at twice the switching frequency (30 kHz) is 0, and the fifth inductor Ln2 and the fourth capacitor Cn2 satisfy the following switching frequency formula,

[0094]

[0095] where 2f sw represents twice the switching frequency, Ln2 represents the inductance of the fifth inductor, and Cn2 represents the capacitance value of the fourth capacitor.

[0096] And because a twice-switching-frequency parallel impedance is formed between the fifth capacitor Cr2 of the second capacitor component 473 of the transformation system 1b in this embodiment and the sixth inductor Lg2, and a third impedance (i.e., the twice-switching-frequency parallel impedance) is jointly generated. The third impedance generated by the fifth capacitor Cr2 of the second capacitor component 473 and the sixth inductor Lg2 at twice the switching frequency (30 kHz) is infinite, so that the gain of the transformation system 1b in this embodiment at twice the switching frequency is lower, thereby preventing the current ripple excitation generated by the transformation system 1b at twice the switching frequency from being transmitted, and from Figure 11From the Bode plot of the amplified bridge arm voltage on the left side to the grid-connected current, it can be clearly seen that the gain of the conversion system 1b in this embodiment at twice the switching frequency is -85.9 dB, while the gain of the traditional conversion system at twice the switching frequency is -73.5 dB. Therefore, it can be known that the gain of the conversion system 1b in this embodiment at twice the switching frequency is 12.4 dB smaller than that of the traditional conversion system at twice the switching frequency. Thus, it can be known that the filtering ability of the conversion system 1b in this embodiment at twice the switching frequency is stronger than that of the traditional conversion system at twice the switching frequency. In addition, the sixth capacitor Cn2_r of the second capacitor component 473 of the second resonant filtering branch 47 and the seventh inductor Ln2_r form a sub-series impedance at the switching frequency, and jointly generate a fourth impedance (i.e., the sub-series impedance at the switching frequency). Among them, the fourth impedance generated by the sixth capacitor Cn2_r of the second capacitor component 473 and the seventh inductor Ln2_r at twice the switching frequency is 0, which can improve the effect of the deterioration of the high-frequency part attenuation caused by increasing the sub-parallel resonant impedance at twice the switching frequency compared with the original scheme, so that the high-frequency part has the same filtering effect as the traditional conversion system 1'. Please refer to Figure 11 Frequency from 3X10 6 -1X10 8 Hz, the curves of the high-frequency parts of the two coincide, and thus have the same suppression effect on EMI, reducing the problems caused by EMI.

[0097] Please refer to Figure 12 and cooperate with Figure 10 , where Figure 12 is Figure 10 the waveform diagram of the external X capacitor - the key branch current inside the module of the conversion system shown. Figure 12 It shows the waveform relationship between the currents flowing into the first trap filter 43, the second trap filter 46, and the internal X capacitor Cx_in and the external X capacitor Cx_out when the conversion system 1b is at twice the switching frequency (30 kHz). As Figure 12 shown, when the external leakage inductance Lt of the conversion system 1b in this embodiment is fixed, the currents flowing into the first trap filter 43, the second trap filter 46, and the internal X capacitor Cx_in do not increase due to the increase in the capacitance value of the external X capacitor Cx_out. Therefore, it can be known that the currents of the first trap filter 43, the second trap filter 46, and the internal X capacitor Cx_in of the conversion system 1b of the present invention are all very stable and are not easily affected by changes in external parameters. In addition, from Figure 12 it can be seen that the current value flowing into the second trap filter 46 is almost fixed at 4 Arms. Since the current value is very stable, the inductance value of the fifth inductor Ln2 and the capacitance value of the fourth capacitor Cn2 in the second trap filter 46 are easier to select and design.

[0098] Of course, in addition to including one notch filter and one resonant filter branch as shown in the first and second embodiments above, or including two notch filters and two resonant filter branches as shown in the third embodiment above, the conversion system of the present invention may further include a greater number of notch filters and resonant filter branches. Please refer to Figure 13 , which is a schematic circuit diagram of the conversion system of the fourth preferred embodiment of the present invention. The conversion system 1c of this embodiment is similar to Figure 4 The conversion system 1 shown. In this embodiment, the conversion system 1c includes N notch filters, N resonant filter branches, and N inductors connected in parallel with the corresponding resonant filter branches. Each notch filter is electrically coupled between the second terminal 52 of the first inductor Linv and the common connection point N, and the N notch filters are connected in parallel with each other. The N inductors connected in parallel with the corresponding resonant filter branches are sequentially connected in series between the second terminal 52 of the first inductor Linv and the second terminal 42 of the filter circuit 4. The filtering ability of the conversion system 1c of this embodiment at N times the switching frequency is stronger than that of the traditional conversion system at N times the switching frequency. However, its circuit structure and operation mode are similar to Figure 4 The conversion system 1 shown, so it will not be elaborated here.

[0099] In summary, the conversion system of the present invention includes a first resonant filter branch and a second inductor connected in parallel. The impedance generated by the first capacitor component of the first resonant filter branch and the second inductor at the switching frequency is infinite, so that the gain of the conversion system of the present invention at the switching frequency is low, thereby preventing the current ripple generated at the switching frequency of the conversion system from being transmitted out. Therefore, it can be seen that the filtering ability of the conversion system of the present invention at the switching frequency is stronger than that of the traditional conversion system at the switching frequency. In addition, the impedance generated by the first capacitor component of the first resonant filter branch and the fourth inductor at the switching frequency is 0, which can improve the phenomenon that the high-frequency part attenuation becomes worse due to the parallel impedance at the switching frequency. Therefore, the conversion system of the present invention can have the same filtering effect as the traditional conversion system at high frequencies, and thus there is no electromagnetic interference problem at high frequencies. Further, the currents flowing into the first notch filter, the first resonant filter branch, and the internal X capacitor in the conversion system of the present invention are all very stable and are not easily affected by external parameter changes, thereby suppressing resonance. Therefore, the conversion system of the present invention can use an internal X capacitor with a lower capacitance value to achieve the benefits of reducing cost and volume and increasing reliability. Moreover, the conversion system of the present invention can further allow errors to occur in the inductance of the fourth inductor and the capacitance value of the first capacitor component of the first resonant filter branch while maintaining a certain degree of filtering ability.

Claims

1. A conversion system is electrically coupled to a power grid. The conversion system has a switching frequency and includes: A conversion circuit for AC-DC conversion; and A filter circuit having a first end and a second end. The first end of the filter circuit is electrically coupled to the conversion circuit, and the second end of the filter circuit is electrically coupled to the power grid. The filter circuit filters AC electrical energy and includes: A first inductor having a first end and a second end. The first end of the first inductor is electrically coupled to the first end of the filter circuit; A second inductor having a first end and a second end. The first end of the second inductor is electrically coupled to the second end of the first inductor, and the second end of the second inductor is electrically coupled to the second end of the filter circuit; A first notch filter having a first end and a second end. The first end of the first notch filter is electrically coupled to the second end of the first inductor and the first end of the second inductor. The second end of the first notch filter is electrically coupled to the second end of the second inductor and the second end of the filter circuit via an internal X capacitor. The first notch filter includes a third inductor and a first capacitor connected in series; and A first resonant filtering branch, having a first end and a second end, the first end of the first resonant filtering branch being electrically coupled to the second end of the first inductor and the first end of the second inductor, the second end of the first resonant filtering branch being electrically coupled to the second end of the second inductor and the second end of the filtering circuit, and the first resonant filtering branch including a first capacitor component and a fourth inductor connected in series, wherein, The first capacitor component includes a second capacitor and a third capacitor. One end of the second capacitor is electrically coupled to the first end of the first resonant filter branch. The third capacitor is electrically coupled between the other end of the second capacitor and the fourth inductor. The second inductor and the second capacitor together generate a first impedance. The first impedance of the second inductor and the second capacitor at the switching frequency is infinite.

2. The transformation system according to claim 1, wherein, The fourth inductor and the third capacitor together generate a second impedance. The second impedance of the fourth inductor and the third capacitor at the switching frequency is 0.

3. The transformation system according to claim 1, wherein, The third inductor and the first capacitor of the first notch filter together generate a first notch impedance. The first notch impedance of the first notch filter at the switching frequency is 0.

4. The transformation system according to claim 1, wherein The filter circuit further includes a second notch filter having a first end and a second end. The first end of the second notch filter is electrically coupled to the first end of the first notch filter, and the second end of the second notch filter is electrically coupled to the second end of the first notch filter. The second notch filter includes a fifth inductor and a fourth capacitor connected in series.

5. The transformation system according to claim 4, wherein, The fifth inductor and the fourth capacitor of the second notch filter together generate a second notch impedance. The second notch impedance of the second notch filter at twice the switching frequency is 0.

6. The transformation system according to claim 4, wherein, The filter circuit further includes a sixth inductor and a second resonant filter branch. The sixth inductor has a first end and a second end. The first end of the sixth inductor is electrically coupled to the second end of the second inductor, and the second end of the sixth inductor is electrically coupled to the second end of the filter circuit. The second resonant filter branch has a first end and a second end. The first end of the second resonant filter branch is electrically coupled to the first end of the sixth inductor, and the second end of the second resonant filter branch is electrically coupled to the second end of the sixth inductor. The second resonant filter branch includes a second capacitor component and a seventh inductor connected in series.

7. The transformation system according to claim 6, wherein, The second capacitor component includes a fifth capacitor and a sixth capacitor. One end of the fifth capacitor is electrically coupled to the first end of the second resonant filter branch. The sixth capacitor is electrically coupled between the other end of the fifth capacitor and the seventh inductor. The sixth inductor and the fifth capacitor together generate a third impedance, and the third impedance of the sixth inductor and the fifth capacitor at twice the switching frequency is infinite.

8. The transformation system according to claim 7, wherein, The seventh inductor and the sixth capacitor together generate a fourth impedance, and the fourth impedance of the seventh inductor and the sixth capacitor at twice the switching frequency is 0.

9. The transformation system according to claim 1, wherein The filter circuit further includes a damping branch having a first end and a second end. The first end of the damping branch is electrically coupled to the first end of the first notch filter, and the second end of the damping branch is electrically coupled to the second end of the first notch filter. The damping branch includes a damping resistor and a damping capacitor connected in series.

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