Common-mode and differential-mode integrated reactor suitable for interleaved parallel connection of converters

Abstract

A common-mode and differential-mode integrated reactor suitable for interleaved parallel connection of a converter is provided with at least two iron core columns (1a) and (1b) with windings and at least one iron core column (2) without windings, the windings (3a) and (3b) installed on the at least two iron core columns with the windings are wound with the same number of turns in the same direction, and the windings (3a) and (3b) are wound with the same number of turns in the same direction. The at least two iron core columns (1a) and (1b) with the windings require an air gap (4) according to a differential mode inductance value, the iron core column (2) without the winding is provided with an air gap (6) according to a common mode inductance value, and the at least two iron core columns (1a) and (1b) with the windings and the at least one iron core column (2) without the winding are communicated through an iron yoke (5) to form the integrated iron core reactor.

Description

Technical Field

[0001] This utility model relates to the field of reactors, and more specifically, to a common-mode and differential-mode integrated reactor suitable for alternating parallel connection of converters. Background Technology

[0002] Power electronic converters are widely used power conversion devices in motor drives, frequency converters, and new energy inverters. The reactors on the bridge arm side of the converter are a crucial component, suppressing output ripple current and smoothing voltage waveforms. The performance, size, and weight of the reactors are very important design parameters for converters. Especially when power electronic converters are used in high-power applications, multiple modules often need to be connected in parallel, in which case the reactors also serve the function of parallel balancing.

[0003] When multiple converter modules are connected in an interleaved parallel configuration, each module needs to be connected in parallel with a reactor at the output. In this mode, the converter modules use a carrier-interleaved modulation scheme, so the fundamental and some higher-order components of the resulting ripple current can cancel each other out, resulting in a smoother output waveform and significantly reduced high-order ripple injected into the load or grid. However, each reactor still needs to withstand a large ripple current. To reduce the ripple current, the inductance needs to be increased. Under the specified rated current conditions, increasing the inductance means increasing the core size and the number of winding turns, inevitably exceeding the expected size and weight of the reactor. Furthermore, an excessively large inductance will cause a significant drop in output voltage under rated current conditions, potentially exceeding system specifications.

[0004] Due to limitations in device switching frequency, switching losses, and heat dissipation capacity, the switching frequency in large-capacity converters needs to be appropriately reduced. Under low switching frequency conditions, the inductance of the reactor also needs to be appropriately increased to meet ripple suppression requirements, while simultaneously avoiding voltage drops caused by excessive inductance. This presents conflicting constraints on the reactor, making it difficult to find a compromise in reactor design. In some cases, reactors with soft-saturation characteristics are used, resulting in a larger inductance at low load currents and core saturation at high load currents, thus reducing the inductance and mitigating the adverse effects of high inductance. However, core saturation at this point distorts the current waveform and causes additional losses to the reactor core.

[0005] In practice, when converters are connected in alternating parallel configurations, there are two different current components: the low-frequency component output by the converter and the switching ripple component that needs to be suppressed. The low-frequency component that needs to be output is the common-mode component, while the switching ripple component that needs to be suppressed includes both common-mode and differential-mode components. The fundamental frequency of the switching frequency, which accounts for the largest proportion, is the differential-mode component. If an integrated reactor can be designed, its common-mode inductance and differential-mode inductance can be designed separately, and it can have a large differential-mode inductance to suppress switching ripple, while at the same time the common-mode inductance is small and does not generate excessive low-frequency voltage drop. This design can be used in the case of alternating parallel configurations of converters. Summary of the Invention

[0006] The purpose of this invention is to provide a common-mode and differential-mode integrated reactor suitable for alternating parallel connection of converters, which can provide a larger differential-mode inductance and a smaller common-mode inductance, so as to solve the dilemma of difficulty in finding a compromise in the value of inductance when alternating parallel connection is used.

[0007] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0008] A common-mode and differential-mode integrated reactor suitable for alternating parallel connection of converters is characterized by having at least two wound iron core columns (1a) and (1b) and at least one unwound iron core column (2). The two wound iron core columns (1a) and (1b) have equal cross-sectional areas and are wound with the same number of turns (3a) and (3b) in the same direction. Air gaps (4) are provided on the at least two wound iron core columns (1a) and (1b), and air gaps (6) are provided on the one unwound iron core column (2). The at least two wound iron core columns (1a) and (1b) and at least one unwound iron core column (2) are connected by a yoke (5) to form an integrated iron core reactor.

[0009] The lower limit of the number of turns of the windings (3a) and (3b) on the at least two wound iron core columns (1a) and (1b) of the reactor is equal to the maximum differential mode voltage amplitude at the alternating output terminal of the converter multiplied by the half-cycle duration of the differential mode voltage fundamental wave divided by the product of the cross-sectional area of ​​the iron core column (1a) and (1b) and the available magnetic flux density, and the upper limit is no more than twice the calculated value of the lower limit.

[0010] The lower limit of the total length of the air gap (4) on the at least two wound iron core columns (1a) and (1b) of the reactor is equal to the product of the square of the number of turns of the winding (3a) or (3b) on the at least two wound iron core columns (1a) and (1b) and the cross-sectional area of ​​the at least two wound iron core columns (1a) or (1b), multiplied by the air permeability and divided by the differential mode inductance of the reactor. The upper limit is no more than twice the calculated value of the lower limit.

[0011] The lower limit of the total length of the air gap (6) on the unwound iron core column (2) of the reactor is equal to the product of the square of the number of turns of the winding (3a) or (3b) on the at least two wound iron core columns (1a) and (1b) and the cross-sectional area of ​​the unwound iron core column (2), multiplied by the air permeability, divided by twice the common mode inductance of the reactor, and then subtracted by half of the air gap (4) on the at least two wound iron core columns (1a) and (1b); the upper limit does not exceed twice the calculated value of the lower limit.

[0012] The common-mode and differential-mode integrated reactor is characterized in that the effective cross-sectional area of ​​the yoke (5) of the reactor is the larger of the cross-sectional area of ​​the wound core column (1a) or (1b) and the cross-sectional area of ​​the unwound core column (2).

[0013] Beneficial effects of this utility model

[0014] According to the technical solution proposed in this utility model, when the converter is N sets of interleaved parallel circuits, a common-mode and differential-mode integrated reactor with N windings is designed accordingly. It has at least N wound iron core columns and at least one unwound iron core column. Depending on the actual magnetic circuit distribution, one or more unwound iron core columns can also be set. All iron core columns are connected through a yoke to form an integrated reactor. When the N outputs of the converter each pass through the N-winding common-mode and differential-mode integrated reactor, the magnetic field formed by the differential-mode current in the N output currents of the converter passes through the yoke. The magnetic field of each wound iron core column is completely canceled out after passing through the yoke, so the magnetic field of each wound iron core column is only confined to the iron core column itself, and its magnetic circuit length is approximately equal to the air gap length of the iron core column. When the magnetic field formed by the common mode current in the output current of the N groups of the converter passes through the yoke, it cannot be canceled out. After being superimposed, it forms a closed magnetic circuit through the unwound iron core column. Therefore, the magnetic circuit of each winding includes both its own iron core column and the unwound iron core column, and its magnetic circuit length is approximately equal to the air gap length of its own iron core column plus the value of the air gap length of the unwound iron core column converted according to the iron core column area ratio. It is evident that the magnetic circuit length of the reactor differs for common-mode current and differential-mode current; the differential-mode current has a shorter magnetic circuit length, while the common-mode current has a longer magnetic circuit length. The inductance is inversely proportional to the magnetic circuit length, allowing the reactor to simultaneously possess a large differential-mode inductance and a small common-mode inductance. This makes it highly suitable for applications involving alternating parallel operation of converters. A larger differential-mode inductance facilitates current balancing among the N outputs of the converter and helps suppress switching ripple current. Conversely, a smaller common-mode inductance is beneficial for reducing the lower limit of the rated current converter output voltage drop. Because the proposed technical solution is an integrated structure, and the common-mode and differential-mode inductances can be designed separately, compared to conventional N independent reactors, it significantly reduces the reactor's size and weight, saving materials and lowering costs. Attached Figure Description

[0015] like Figure 1 The diagram shown is a magnetic circuit diagram of the reactor of this utility model.

[0016] like Figure 2 The diagram shown is a specific embodiment of this utility model.

[0017] like Figure 3 The diagram shown is a schematic representation of a specific embodiment of the iron core of this utility model.

[0018] like Figure 4 The diagram shown is a schematic representation of the overall design of the core and windings after installation. Detailed Implementation

[0019] The technical implementation scheme of this utility model is described in detail below with reference to the accompanying drawings, such as... Figure 1 The diagram shown is a schematic diagram of the reactor of this utility model. It is characterized by having at least two wound iron core columns (1a) and (1b) and at least one unwound iron core column (2). The two wound iron core columns (1a) and (1b) have equal cross-sectional areas and are wound with the same number of turns (3a) and (3b) in the same direction. An air gap (4) is opened on both the two wound iron core columns (1a) and (1b), and an air gap (6) is also opened on the unwound iron core column (2). The two wound iron core columns (1a) and (1b) and at least one unwound iron core column (2) are connected by an iron yoke (5) to form an integrated iron core reactor.

[0020] The lower limit of the number of turns of the windings (3a) and (3b) on at least two wound iron core columns (1a) and (1b) of the reactor is equal to the maximum differential mode voltage amplitude at the alternating output terminal of the converter multiplied by the half-cycle duration of the differential mode voltage fundamental wave divided by the product of the cross-sectional area of ​​the iron core columns (1a) and (1b) and the available magnetic flux density, and the upper limit of the number of turns does not exceed twice the calculated value of this lower limit.

[0021] Taking a 380V alternating converter as an example, if the DC-side voltage of the converter is 750V, then the duty cycle of the converter at the zero-crossing point is 50%, and each reactor winding bears one-quarter of the differential-mode voltage of the DC-side voltage, i.e., 187.5V. If the switching frequency of the converter is 6400Hz, the duration of the fundamental half-cycle of the differential-mode voltage is half a cycle of the switching frequency, i.e., 78.125 microseconds. If the cross-sectional area of ​​the core column is 0.003 square meters, and the magnetic flux density is taken as 0.12 Tesla, then the number of winding turns can be taken as 187.5V × 78.125 microseconds ÷ (0.003 square meters × 0.12 Tesla) ≈ 41 turns, which shall not exceed twice this calculated value.

[0022] The lower limit of the total length of the air gap (4) on the at least two wound iron core columns (1a) and (1b) of the reactor is equal to the product of the square of the number of turns of the winding (3a) or (3b) on the at least two wound iron core columns (1a) and (1b) and the cross-sectional area of ​​the at least two wound iron core columns (1a) or (1b), multiplied by the air permeability and divided by the differential mode inductance of the reactor. The upper limit of the total length of the air gap (4) does not exceed twice the calculated value of this lower limit.

[0023] The lower limit of the total length of the air gap (6) on the unwound iron core column (2) of the reactor is equal to the product of the square of the number of turns of the winding (3a) or (3b) on the at least two wound iron core columns (1a) and (1b) and the cross-sectional area of ​​the unwound iron core column (2), multiplied by the air permeability, divided by twice the common mode inductance of the reactor, and then subtracted by half of the air gap (4) on the at least two wound iron core columns (1a) and (1b). The upper limit of the total length of the air gap (6) does not exceed twice the calculated value of this lower limit.

[0024] Taking the aforementioned 380V two-group interleaved converter as an example, based on the previously calculated winding turns of 41 turns and core column cross-sectional area of ​​0.003 square meters, if the cross-sectional area of ​​core column (2) is also 0.003 square meters, and the differential mode inductance of the reactor is required to be 1100 microhenries and the common mode inductance to be 300 microhenries, then the total length of the air gap (4) on core columns (1a) and (1b) should be 41. 2 ×0.003 square meters × 4π × 10 -7 Henry / meter ÷ 1100 microhenries ≈ 0.0058 meters, where 4π × 10 -7 Henry / meter is the magnetic permeability of vacuum or air; the total length of the air gap (6) on the top of the iron core column (2) is equal to 41. 2 ×0.003 square meters × 4π × 10 -7 Henry / meter ÷ (2 × 300 microhenries) - 0.0058 meters ÷ 2 ≈ 0.0077 meters.

[0025] The common-mode and differential-mode integrated reactor is characterized in that the effective cross-sectional area of ​​the yoke (5) of the reactor is the larger of the cross-sectional area of ​​the wound core column (1a) or (1b) and the cross-sectional area of ​​the unwound core column (2). This is mainly to ensure that the magnetic flux density on the yoke cross section does not exceed that of any core column, thus avoiding additional core losses.

[0026] like Figure 2The diagram shows a specific implementation scheme of this invention applied to a three-group interleaved converter. In this scheme, three wound core columns and two unwound core columns are designed. The three wound core columns have the same number of turns and the same winding direction. Each core column has two air gaps, while each of the two unwound core columns has three air gaps. The converter output is connected to terminals A, B, and C of the windings, while terminals a, b, and c can be short-circuited together. For the differential-mode components of the current entering A, B, and C, their magnetic fields cancel each other out in the core, therefore the magnetic circuit of the differential-mode current is equal to the magnetic circuit length of each core column. The common-mode components of the current entering A, B, and C cannot cancel out, and ultimately form a closed magnetic circuit through the yoke and the unwound core columns. The circuit length is equal to the magnetic circuit length of each core column plus the magnetic circuit length of the unwound core column. The inductance is inversely proportional to the magnetic circuit length; therefore, this design results in a large differential-mode inductance and a small common-mode inductance.

[0027] like Figure 3 The figure shows a specific implementation scheme for the iron core when applied to three sets of alternating converters. In practical applications, low-loss oriented high-permeability silicon steel sheets are selected, preferably with a thickness of less than 0.23 mm. Referring to the loss curve, taking an 8 kHz switching frequency as an example, under air-cooled heat dissipation and 50% intermittent operation mode, the available magnetic flux density of the silicon steel sheet is taken as 1250 Gauss. The calculated value is appropriately relaxed to reserve space for structural installation.

[0028] like Figure 4 The diagram shows the overall installation scheme of a common-mode and differential-mode integrated reactor suitable for three sets of interleaved converters connected in parallel. Due to the integrated design of differential and common modes, the reactor has a very compact overall shape. Compared with using three separate single-phase reactors, the size is significantly reduced, which can save materials and reduce the overall weight of the reactor.

Claims

1. A common-mode and differential-mode integrated reactor suitable for alternating parallel operation of converters, characterized in that: The device comprises at least two wound core columns (1a) and (1b) and at least one unwound core column (2). The two wound core columns (1a) and (1b) have equal cross-sectional areas and are wound with the same number of turns (3a) and (3b) in the same direction. Air gaps (4) are provided on the at least two wound core columns (1a) and (1b), and air gaps (6) are provided on the one unwound core column (2). The at least two wound core columns (1a) and (1b) and at least one unwound core column (2) are connected by a yoke (5) to form an integrated core reactor.

2. The common-mode and differential-mode integrated reactor according to claim 1, characterized in that the lower limit of the number of turns of the windings (3a) and (3b) on the at least two wound iron core columns (1a) and (1b) of the reactor is equal to the maximum differential-mode voltage amplitude at the alternating output terminal of the converter multiplied by the half-cycle duration of the differential-mode voltage fundamental wave divided by the product of the cross-sectional area of ​​the iron core columns (1a) and (1b) and the available magnetic flux density, and the upper limit does not exceed twice the calculated value of the lower limit.

3. The common-mode and differential-mode integrated reactor according to claim 1, characterized in that: The lower limit of the total length of the air gap (4) on the at least two wound iron core columns (1a) and (1b) of the reactor is equal to the product of the square of the number of turns of the winding (3a) or (3b) on the at least two wound iron core columns (1a) and (1b) and the cross-sectional area of ​​the at least two wound iron core columns (1a) or (1b), multiplied by the air permeability and divided by the differential mode inductance of the reactor. The upper limit is no more than twice the calculated value of the lower limit.

4. The common-mode and differential-mode integrated reactor according to claim 1, characterized in that the lower limit of the total length of the air gap (6) opened on one unwound iron core column (2) of the reactor is equal to the product of the square of the number of turns of the winding (3a) or (3b) on the at least two wound iron core columns (1a) and (1b) and the cross-sectional area of ​​the unwound iron core column (2), multiplied by the air permeability, divided by twice the common-mode inductance of the reactor, and then subtracted by half of the air gap (4) opened on the at least two wound iron core columns (1a) and (1b); the upper limit does not exceed twice the calculated value of the lower limit.

5. The common-mode and differential-mode integrated reactor according to claim 1, characterized in that: The effective cross-sectional area of ​​the yoke (5) of the reactor is the larger of the cross-sectional area of ​​the wound core column (1a) or (1b) and the cross-sectional area of ​​the unwound core column (2).

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