Control system for current sharing of parallel inverters

Abstract

The utility model discloses a control system for current sharing of parallel inverters, which comprises a plurality of parallel inverters and a voltage outer loop controller, each inverter comprises a bridge circuit consisting of switch tubes S1, S2, S3 and S4, and each inverter is provided with an independent current closed loop control unit. And the current closed-loop control unit comprises an independent current inner loop which is arranged in the inverter and is used for respectively controlling the current of each inverter. And dividing the current reference value calculated by the voltage outer loop controller into N equal parts as the current reference value of the current loop in the inverter. Closed-loop control is respectively carried out on the current of the plurality of inverters, so that the current sharing among the inverters is ensured.

Description

Technical Field

[0001] The utility model relates to an inverter, in particular to a current-sharing control system for parallel inverters. Background Art

[0002] Inverters convert direct current into alternating current and are widely used in civil and industrial fields.

[0003] In the prior art:

[0004] A typical inverter circuit is Figure 1 As shown, the input is a DC voltage, and by controlling the full bridge in a certain way, an AC voltage can be output.

[0005] When used in high-power or high-current scenarios, a single inverter bridge may cause the switching tube to bear greater current stress and generate severe heat. Therefore, multiple inverters can be connected in parallel to allow each inverter to share the current. Figure 2 The structure shown is two inverters connected in parallel.

[0006] Existing technology and defects:

[0007] The existing technology performs synchronous control on all inverters. However, since the impedance of the inverters cannot be completely consistent, it will cause uneven current between the inverters, that is, the current on different inverters is different, causing current stress to be concentrated on a certain inverter.

[0008] In view of this, the present utility model is proposed. Utility Model Content

[0009] The purpose of the utility model is to provide a control system for current sharing of parallel inverters to solve the above technical problems existing in the prior art.

[0010] The purpose of this utility model is achieved through the following technical solutions:

[0011] The utility model discloses a control system for current sharing of parallel inverters, comprising a plurality of parallel inverters and a voltage outer loop controller, wherein each inverter comprises a bridge circuit composed of four switching tubes;

[0012] The switching tube includes:

[0013] S1: MOS tube between the positive pole of the input DC side and the L pole of the output AC side;

[0014] S2: MOS tube between the negative pole of the input DC side and the L pole of the output AC side;

[0015] S3: MOS tube between the positive pole of the input DC side and the N pole of the output AC side;

[0016] S4: MOS tube between the negative pole of the input DC side and the N pole of the output AC side;

[0017] Each inverter is equipped with a separate current closed-loop control unit.

[0018] Compared with the prior art, the control system for current sharing of parallel inverters provided by the present invention ensures current sharing among the inverters by performing closed-loop control on the currents of multiple inverters respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a typical inverter circuit schematic diagram in the prior art;

[0020] Figure 2 This is a schematic diagram of the structure of two inverters connected in parallel in the prior art;

[0021] Figure 3 This is a schematic diagram of S1 and S4 being turned on simultaneously in an embodiment of the present utility model;

[0022] Figure 4 This is a schematic diagram of S2 and S3 being turned on simultaneously in an embodiment of the present utility model;

[0023] Figure 5 This is the control block diagram of the traditional parallel inverter;

[0024] Figure 6 This is a control block diagram proposed in an embodiment of the present utility model;

[0025] Figure 7 Schematic diagram of currents of left and right inverters in the prior art;

[0026] Figure 8 This is a schematic diagram of simulation results using the control method proposed by the present invention in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them, and do not constitute a limitation of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] First, the following terms may be used in this article:

[0029] The term “and / or” means that either or both of them can be realized at the same time. For example, X and / or Y includes both “X” or “Y” and “X and Y”.

[0030] The terms "include", "comprises", "contains", "has" or other descriptions with similar meanings should be interpreted as non-exclusive inclusion.

[0031] The term "consisting of" excludes any technical features not explicitly listed. If used in a claim, this term renders the claim closed, excluding any technical features other than those explicitly listed, except for conventional impurities associated with them. If this term appears only in a clause of a claim, it limits only the elements explicitly listed in that clause; elements listed in other clauses are not excluded from the claim as a whole.

[0032] The contents not described in detail in the examples of this utility model belong to the prior art known to those skilled in the art. If specific conditions are not specified in the examples of this utility model, the experiments were carried out according to conventional conditions in the art or the conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments used in the examples of this utility model are not specified, they are all conventional products that can be purchased commercially.

[0033] The utility model discloses a control system for current sharing of parallel inverters, comprising a plurality of parallel inverters and a voltage outer loop controller, wherein each inverter comprises a bridge circuit composed of four switching tubes;

[0034] The switching tube includes:

[0035] S1: MOS tube between the positive pole of the input DC side and the L pole of the output AC side;

[0036] S2: MOS tube between the negative pole of the input DC side and the L pole of the output AC side;

[0037] S3: MOS tube between the positive pole of the input DC side and the N pole of the output AC side;

[0038] S4: MOS tube between the negative pole of the input DC side and the N pole of the output AC side;

[0039] Each inverter is equipped with a separate current closed-loop control unit.

[0040] The current closed-loop control unit includes a separate current inner loop provided inside the inverter for controlling the current of each inverter respectively.

[0041] N inverters are connected in parallel, and the current reference value calculated by the voltage outer loop controller is divided into N equal parts as the current reference value of the inverter inner current loop.

[0042] Using bipolar drive method:

[0043] When S1 and S4 are turned on at the same time, the bridge voltage Uab = Vdc;

[0044] When S2 and S3 are turned on at the same time, the bridge voltage Uab = -Vdc;

[0045] By adjusting the driving time of the switch tube, the ratio of Vdc and -Vdc in Uab is distributed, thereby adjusting the output voltage.

[0046] When the driving PWM is given as SPWM, the output voltage is a sinusoidal AC voltage.

[0047] A separate current inner loop is introduced inside the inverter to control the current of each inverter separately to achieve current sharing.

[0048] N inverters are connected in parallel, and the current reference value calculated by the voltage outer loop controller is divided into N equal parts as the current reference value of the inverter inner current loop.

[0049] In summary, the control system for current sharing of parallel inverters according to the embodiment of the present invention ensures current sharing among the inverters by performing closed-loop control on the currents of the multiple inverters respectively.

[0050] In order to more clearly demonstrate the technical solution and technical effects provided by the present invention, the embodiments of the present invention are described in detail below with reference to specific embodiments.

[0051] Example 1

[0052] The bipolar driving method is taken as an example for explanation.

[0053] Two MOS tubes form a bridge arm, and two bridge arms form a full bridge. The connection between MOS tubes follows certain rules:

[0054] S1: MOS tube between the positive pole of the input DC side and the L pole of the output AC side

[0055] S2: MOS tube between the negative pole of the input DC side and the L pole of the output AC side

[0056] S3: MOS tube between the positive pole of the input DC side and the N pole of the output AC side

[0057] S4: MOS tube between the negative pole of the input DC side and the N pole of the output AC side

[0058] like Figure 3 As shown, when S1 and S4 are turned on at the same time, the bridge voltage Uab = Vdc.

[0059] like Figure 4As shown in the figure, when S2 and S3 are both on, Uab = -Vdc. By adjusting the switching time, the ratio of Vdc to -Vdc in Uab can be adjusted, thus adjusting the output voltage on average. When the drive PWM is set to SPWM, the output voltage is a sinusoidal AC voltage.

[0060] When performing the above control, dual closed-loop control is generally adopted in the prior art, and the current loop feedback takes the total current, that is, the current on the inductor L5 or L10. The specific control block diagram is as follows: Figure 5 shown.

[0061] The utility model introduces a current inner loop into the inverter to control the current of each inverter separately to achieve current sharing. The control block diagram is shown as follows: Figure 6 If there are N inverters connected in parallel, the current reference value calculated by the voltage outer loop controller is divided into N equal parts and used as the current reference value of the inverter's internal current loop.

[0062] Testing and experimental verification

[0063] Taking two inverters in parallel as an example, if the line impedance of the left inverter is set to 0.1Ω and the line impedance of the right inverter is set to 0.2Ω, if Figure 5 In traditional control mode, the current of the two inverters is as follows: Figure 7 As shown in the figure, the left inverter has half the impedance of the right inverter, so its current is twice that of the right inverter, and it bears more current stress.

[0064] If the utility model is adopted Figure 6 The control method shown in the simulation results are as follows Figure 8 As shown in the figure, the currents of the left and right inverters become equal, which verifies the effectiveness of the current sharing of this control method.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or any form of implication that the information constitutes prior art already known to those skilled in the art.

Claims

1. A control system for current sharing of parallel inverters, characterized in that: The invention comprises a plurality of parallel-connected inverters and a voltage outer loop controller, wherein each inverter comprises a bridge circuit composed of four switching tubes; The switching tube includes: S1: MOS tube between the positive pole of the input DC side and the L pole of the output AC side; S2: MOS tube between the negative pole of the input DC side and the L pole of the output AC side; S3: MOS tube between the positive pole of the input DC side and the N pole of the output AC side; S4: MOS tube between the negative pole of the input DC side and the N pole of the output AC side; Each inverter is equipped with a separate current closed-loop control unit.

2. The control system for current sharing of parallel inverters according to claim 1, characterized in that: The current closed-loop control unit includes a separate current inner loop provided inside the inverter for controlling the current of each inverter respectively.

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