Control method for current sharing of parallel inverters

Abstract

The invention discloses a parallel inverter current sharing control method, which comprises a plurality of parallel inverters and a voltage outer loop controller, each inverter comprises a bridge circuit composed of switch tubes S1, S2, S3 and S4, and current sharing among the inverters is ensured by performing closed-loop control on current of the plurality of inverters; by adjusting the driving time of a switching tube, the proportion of Vdc to-Vdc in Uab is distributed, and then the magnitude of the output voltage is adjusted. A current inner ring is independently introduced into the inverter and is used for respectively controlling the current of each inverter so as to realize current sharing. 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 present invention relates to an inverter, and in particular to a current sharing control method 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 switch tube to bear a large 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 prior art performs synchronous control on all inverters, but since the impedance of the inverters cannot be completely consistent, it will cause uneven current between the inverters, that is, the currents on different inverters are different, and the current stress is concentrated on a certain inverter.

[0008] In view of this, the present invention is proposed. Summary of the invention

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

[0010] The objective of the present invention is achieved through the following technical solutions:

[0011] The control method for current sharing of parallel inverters of the present invention comprises a plurality of parallel inverters and a voltage outer loop controller, each inverter comprises a bridge circuit composed of four switch tubes, and current sharing between the inverters is ensured by performing closed-loop control on the currents of the plurality of inverters respectively;

[0012] The switch 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] Using bipolar drive method:

[0018] When S1 and S4 are turned on at the same time, the bridge voltage Uab = Vdc;

[0019] When S2 and S3 are turned on at the same time, the bridge voltage Uab = -Vdc;

[0020] By adjusting the driving time of the switch tube, the ratio of Vdc and -Vdc in Uab is allocated, thereby adjusting the output voltage.

[0021] Compared with the prior art, the control method for current sharing of parallel inverters provided by the present invention performs closed-loop control on the currents of multiple inverters respectively, thereby ensuring current sharing among the inverters. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a typical inverter circuit schematic diagram in the prior art;

[0023] Figure 2 It is a structural schematic diagram of two inverters connected in parallel in the prior art;

[0024] Figure 3 Schematic diagram of S1 and S4 being turned on simultaneously in an embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of S2 and S3 being turned on simultaneously in an embodiment of the present invention;

[0026] Figure 5 This is the control block diagram of the traditional parallel inverter;

[0027] Figure 6 It is a control block diagram proposed in an embodiment of the present invention;

[0028] Figure 7 It is a schematic diagram of currents of left and right inverters in the prior art;

[0029] 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

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0031] First, the terms that may be used in this article are explained as follows:

[0032] The term “and / or” means that either or both of them can be realized at the same time. For example, X and / or Y means both “X” or “Y” and “X and Y”.

[0033] The terms "include", "comprises", "contains", "has" or other similar semantic descriptions should be interpreted as non-exclusive inclusion.

[0034] The term "consisting of..." means excluding any technical feature elements not explicitly listed. If this term is used in a claim, it will make the claim closed, so that it does not contain technical feature elements other than the technical feature elements explicitly listed, except for the conventional impurities related to them. If this term only appears in a clause of a claim, it only limits the elements explicitly listed in the clause, and the elements recorded in other clauses are not excluded from the overall claim.

[0035] The contents not described in detail in the examples of the present invention belong to the prior art known to professionals in the field. If no specific conditions are specified in the examples of the present invention, the conditions are carried out according to the conventional conditions in the field or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used in the examples of the present invention, they are all conventional products that can be purchased commercially.

[0036] The control method for current sharing of parallel inverters of the present invention comprises a plurality of parallel inverters and a voltage outer loop controller, each inverter comprises a bridge circuit composed of four switch tubes, and current sharing between the inverters is ensured by performing closed-loop control on the currents of the plurality of inverters respectively;

[0037] The switch tube includes:

[0038] S1: MOS tube between the positive pole of the input DC side and the L pole of the output AC side;

[0039] S2: MOS tube between the negative pole of the input DC side and the L pole of the output AC side;

[0040] S3: MOS tube between the positive pole of the input DC side and the N pole of the output AC side;

[0041] S4: MOS tube between the negative pole of the input DC side and the N pole of the output AC side;

[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 allocated, 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 inner current loop of the inverter.

[0049] In summary, it can be seen that the control method 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 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 with specific embodiments below.

[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 4 As shown, when S2 and S3 are turned on at the same time, Uab = -Vdc. By adjusting the driving time of the switch tube, the ratio of Vdc and -Vdc in Uab can be allocated, and the output voltage can be adjusted on average. When the driving PWM is given as 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 present invention 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 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 as the current reference value of the inverter 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 Figure 7 As shown in the figure, the left inverter has half the impedance of the right inverter, so the current is twice that of the right inverter, and it bears more current stress.

[0064] If the present invention is adopted Figure 6 The control method shown in the simulation results is as follows Figure 8 As shown, the currents of the left and right inverters become equal, verifying the effectiveness of the current sharing of this control method.

[0065] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope 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 in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A method for controlling current sharing of parallel inverters, characterized in that: It includes multiple parallel inverters and a voltage outer loop controller. Each inverter includes a bridge circuit composed of four switch tubes. The currents of multiple inverters are closed-loop controlled respectively, so as to ensure current sharing among the inverters. The switch 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; Using bipolar drive method: When S1 and S4 are turned on at the same time, the bridge voltage Uab = Vdc; When S2 and S3 are turned on at the same time, the bridge voltage Uab = -Vdc; By adjusting the driving time of the switch tube, the ratio of Vdc and -Vdc in Uab is allocated, thereby adjusting the output voltage.

2. The control method for current sharing of parallel inverters according to claim 1, characterized in that: When the driving PWM is given as SPWM, the output voltage is a sinusoidal AC voltage.

3. The control method for current sharing of parallel inverters according to claim 2, characterized in that: A separate current inner loop is introduced inside the inverter to control the current of each inverter separately to achieve current sharing.

4. The method for controlling current sharing of parallel inverters according to claim 3, characterized in that: 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 inner current loop of the inverter.

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