A dc power transmission system based on a wien rectifier and a control method thereof

Abstract

The application discloses a DC power transmission system based on a Vienna rectifier and a control method thereof. The DC power transmission system comprises a sending end AC system, a sending end rectifier station, a DC line, a receiving end inverter station and a receiving end AC system which are connected in series; the receiving end inverter station adopts fixed DC voltage control; and fixed DC power or fixed DC current control is realized by adjusting the DC voltage of the Vienna rectifier. The application can effectively improve the operation reliability and flexibility of the hybrid DC, and meanwhile, through optimized allocation of capacity, the application can also realize functions such as harmonic compensation and reactive power compensation.

Description

Technical Field

[0001] This invention belongs to the technical field of DC transmission systems, specifically relating to a DC transmission system based on a Vienna rectifier and its control method. Background Technology

[0002] DC power transmission and distribution has evolved to include conventional DC, flexible DC, and hybrid DC topologies. Among them, hybrid DC combines thyristor converters and voltage source converters, effectively leveraging the economic advantages of thyristor converters and the technical advantages of voltage source converters, and represents the latest development trend.

[0003] Compared to thyristor converters, diode rectifiers are less expensive and more reliable. Hybrid DC systems based on diode rectifiers can achieve the same functions as traditional hybrid DC systems; however, because diode rectifiers lack any control mechanisms, the control of hybrid DC systems based on them is inflexible, and the DC voltage will vary with the AC voltage. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a DC transmission system based on a Vienna rectifier and its control method. By introducing a Vienna rectifier at the sending end of a hybrid DC system based on a diode rectifier and cooperating with a corresponding control method, the reliability and flexibility of the hybrid DC system can be effectively improved.

[0005] The first aspect of the present invention is to provide a DC transmission system based on a Vienna rectifier, which includes a sending-end AC system, a sending-end rectifier station, a DC line, a receiving-end inverter station, and a receiving-end AC system connected in series.

[0006] The sending-end rectifier station adopts a hybrid rectifier based on a Vienna rectifier; the hybrid rectifier is composed of a diode rectifier and a Vienna rectifier connected in series on the DC side;

[0007] On the DC side, the sending-end rectifier station is used to control the DC current, and the receiving-end inverter station is used to control the DC voltage.

[0008] Furthermore, the number of diode rectifiers can be one or more, depending on actual needs. For example, one diode rectifier can be connected in series with one Vienna rectifier, or two diode rectifiers can be connected in series with one Vienna rectifier, etc.

[0009] Furthermore, the diode rectifier and the Vienna rectifier are connected to the same or different AC busbars via AC transformers.

[0010] Furthermore, each diode rectifier consists of 6 diode bridge arms, and each Vienna rectifier consists of 6 diode bridge arms and 3 turn-off bridge arms.

[0011] Furthermore, the diode bridge arm in the diode rectifier is composed of multiple diodes connected in series; the diode bridge arm in the Vienna rectifier is composed of multiple diodes connected in series, and the turn-off bridge arm is composed of multiple IGBTs connected in forward and reverse directions.

[0012] Furthermore, within the hybrid rectifier, the capacity configuration of the diode converter and the Vienna rectifier is determined based on actual needs and economic considerations. Case 1: If only DC voltage regulation capability is required in the hybrid rectifier, since the cost of the Vienna rectifier is higher than that of the diode rectifier, over 90% of the capacity is handled by the diode rectifier, and less than 10% by the Vienna rectifier, to improve economic efficiency. Case 2: If harmonic compensation, reactive power compensation, and DC voltage regulation capability are required in the hybrid rectifier, then the diode rectifier and the Vienna rectifier are configured with each accounting for 50% of the capacity. Other cases can be adjusted and adapted based on Cases 1 and 2.

[0013] Furthermore, the receiving-end inverter station adopts a modular multilevel converter, a cascaded multilevel converter, or a thyristor converter.

[0014] Furthermore, the DC line can be an overhead line or a cable, depending on actual needs.

[0015] A second aspect of the present invention is to provide a control method for the aforementioned DC transmission system, wherein the receiving-end inverter station adopts constant DC voltage control; since the diode rectifier in the sending-end rectifier station does not have adjustment capability, constant DC power or constant DC current control is achieved by adjusting the DC voltage of the Vienna rectifier.

[0016] Furthermore, the constant DC control adopts a DC current command value I. dref With DC current measurement value I dmes The difference is used by a PI controller to obtain the DC voltage deviation value ΔU. d ΔU d and Vienna rectifier DC voltage command value U dref After being added together, the new DC voltage command is input to the inner and outer loop controllers of the Vienna rectifier to achieve DC current control; where I dref Obtained through the following formula:

[0017]

[0018] Among them, P ref U is the power command value transmitted from the sending end to the receiving end. dmesi U represents the measured DC voltage of the i-th diode rectifier, where N is the number of diode rectifiers. dmesv This is the measured DC voltage value of the Vienna rectifier.

[0019] Furthermore, for hybrid rectifiers that only require DC voltage regulation capability, Vienna rectifiers only perform constant DC current control; for hybrid rectifiers that require harmonic compensation, reactive power compensation, and DC voltage regulation capability, Vienna rectifiers, in addition to constant DC current control, also employ harmonic compensation and reactive power compensation control functions on the AC side to absorb harmonics emitted by the diode rectifier and compensate for the reactive power required by the diode rectifier.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The proposed DC transmission system and its control method based on Vienna rectifier can effectively improve the operational reliability and flexibility of hybrid DC; at the same time, through optimized capacity configuration, it can also achieve functions such as harmonic compensation and reactive power compensation. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the DC transmission system topology of the present invention;

[0024] Figure 2 This is a schematic diagram of the hybrid rectifier topology based on the Vienna rectifier of the present invention;

[0025] Figure 3 This is a schematic diagram of the modular multilevel converter topology of the present invention;

[0026] Figure 4 This is a schematic diagram of the thyristor converter topology of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Figure 1The figure shows a DC transmission system based on a Vienna rectifier. As can be seen from the figure, the DC transmission system includes a sending-end AC system, a sending-end rectifier station, a DC line, a receiving-end inverter station, and a receiving-end AC system connected in series.

[0029] Sending-end rectifier station adopts such as Figure 2 The hybrid rectifier based on the Vienna rectifier shown in the figure consists of a series connection of diode rectifiers and Vienna rectifiers on the DC side. The number of converters connected in series can be determined according to actual needs, such as one diode rectifier connected in series with one Vienna rectifier, or two diode rectifiers connected in series with one Vienna rectifier. The figure shows an example of two diode rectifiers connected in series with one Vienna rectifier. The diode rectifiers and Vienna rectifiers are connected to the same or different AC busbars through AC transformers. Each diode rectifier consists of 6 diode arms, and each Vienna rectifier consists of 6 diode arms and 3 turn-off arms.

[0030] Diode rectifiers use multiple diodes connected in series to form a bridge arm, enabling high-voltage, high-capacity applications. Similarly, the diode bridge arm in Vienna rectifiers is formed by multiple diodes connected in series, while the turn-off bridge arm is formed by multiple IGBTs connected in forward and reverse series.

[0031] In a hybrid rectifier, the capacity configuration of the diode converter and the Vienna rectifier can be determined based on actual needs and economic considerations. Case 1: If only DC voltage regulation capability is required in the hybrid rectifier, since the cost of the Vienna rectifier is higher than that of the diode rectifier, over 90% of the capacity should be handled by the diode rectifier, and less than 10% by the Vienna rectifier, to improve economic efficiency. Case 2: If harmonic compensation, reactive power compensation, and DC voltage regulation capability are required in the hybrid rectifier, then the diode rectifier and the Vienna rectifier can be configured with each accounting for 50% of the capacity. Other cases can be adjusted based on Cases 1 and 2.

[0032] The receiving-end inverter station can adopt various converter types, such as modular multilevel converters (see...). Figure 3 ), cascaded multilevel converters, thyristor converters (see...) Figure 4 DC lines can be overhead lines or cables, depending on actual needs.

[0033] The control method for the DC transmission system based on the Vienna rectifier described above uses constant DC voltage control at the receiving-end inverter station. Since the diode rectifier in the sending-end rectifier station does not have adjustment capability, constant DC power or constant DC current control is achieved by adjusting the DC voltage of the Vienna rectifier.

[0034] The aforementioned constant DC control uses a DC current command value I.dref With DC current measurement value I dmes The difference is used by a PI controller to obtain the DC voltage deviation value ΔU. d ΔU d and Vienna rectifier DC voltage command value U dref After being added together, the new DC voltage command is input to the inner and outer loop controllers of the Vienna rectifier to achieve DC current control; where I dref Obtained through the following formula:

[0035]

[0036] Among them, P ref U is the power command value transmitted from the sending end to the receiving end. dmesi U represents the measured DC voltage of the i-th diode rectifier, where N is the number of diode rectifiers. dmesv This is the measured DC voltage value of the Vienna rectifier.

[0037] In scenario 1, the Vienna rectifier only performs constant DC current control. In scenario 2, in addition to constant DC current control, the Vienna rectifier also employs harmonic compensation and reactive power compensation control functions on the AC side to absorb the harmonics emitted by the diode rectifier and compensate for the reactive power required by the diode rectifier.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for a DC transmission system based on a Vienna rectifier, characterized in that, The DC transmission system includes a sending-end AC system, a sending-end rectifier station, a DC line, a receiving-end inverter station, and a receiving-end AC system connected in series. The sending-end rectifier station adopts a hybrid rectifier based on a Vienna rectifier; the hybrid rectifier is composed of a diode rectifier and a Vienna rectifier connected in series on the DC side; On the DC side, the sending-end rectifier station is used to control the DC current, and the receiving-end inverter station is used to control the DC voltage. In the hybrid rectifier, the capacity configuration of the diode converter and the Vienna rectifier is determined based on actual needs and economic considerations. Case 1: If only DC voltage regulation capability is required in the hybrid rectifier, since the cost of the Vienna rectifier is higher than that of the diode rectifier, more than 90% of the capacity is handled by the diode rectifier, and less than 10% by the Vienna rectifier, to improve economic efficiency. Case 2: If the hybrid rectifier requires harmonic compensation, reactive power compensation, and DC voltage regulation capability, then the diode rectifier and the Vienna rectifier are configured to each account for 50% of the capacity. The control method of the DC transmission system is as follows: the receiving-end inverter station adopts constant DC voltage control; constant DC power or constant DC current control is achieved by adjusting the DC voltage of the Vienna rectifier; for hybrid rectifiers that only require DC voltage regulation capability, the Vienna rectifier only performs constant DC current control; for hybrid rectifiers that require harmonic compensation, reactive power compensation and DC voltage regulation capability, the Vienna rectifier, in addition to constant DC current control, also adopts harmonic compensation and reactive power compensation control functions on the AC side to absorb the harmonics emitted by the diode rectifier and compensate for the reactive power required by the diode rectifier.

2. The control method according to claim 1, characterized in that, The number of diode rectifiers can be one or more, depending on actual needs.

3. The control method according to claim 1, characterized in that, The diode rectifier and the Vienna rectifier are connected to the same or different AC busbars via AC transformers.

4. The control method according to claim 1, characterized in that, Each diode rectifier consists of 6 diode bridge arms, and each Vienna rectifier consists of 6 diode bridge arms and 3 turn-off bridge arms.

5. The control method according to claim 4, characterized in that, The diode bridge arm in the diode rectifier is composed of multiple diodes connected in series; the diode bridge arm in the Vienna rectifier is composed of multiple diodes connected in series, and the turn-off bridge arm is composed of multiple IGBTs connected in forward and reverse directions.

6. The control method according to claim 1, characterized in that, The receiving-end inverter station adopts a modular multilevel converter, a cascaded multilevel converter, or a thyristor converter.

7. The control method according to claim 1, characterized in that, The aforementioned constant DC control uses a DC current command value I. dref With DC current measurement value I dmes The difference is used by a PI controller to obtain the DC voltage deviation value ΔU. d ΔU d and Vienna rectifier DC voltage command value U dref After being added together, the new DC voltage command is input to the inner and outer loop controllers of the Vienna rectifier to achieve DC current control; where I dref Obtained through the following formula: in, P ref This refers to the power command value transmitted from the sending end to the receiving end. U dmesi For the first i DC voltage measurement value of a diode rectifier N The number of diode rectifiers. U dmesv This is the measured DC voltage value of the Vienna rectifier.

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