A design method for a sending-end station based on diode rectification and current source converter

Abstract

The present invention discloses a method for designing a sending-end station based on diode rectification and a current source converter, and relates to the technical field of stable external transmission application of new energy. The method includes parameter design, black start design, and DC fault ride-through design. The parameter design is mainly implemented based on the following constraints: diode rectification quantity constraint, current source converter modulation ratio constraint, current source converter DC voltage constraint, and DC fault ride-through constraint. The black start design enables the startup of an offshore new energy station by switching between constant current and constant voltage control at a receiving-end station. The DC fault ride-through design takes into account parameter errors generated by AC energy switching, and suppresses DC fault current by reversing the DC voltage of the current source converter. The AC fault ride-through design suppresses modulation wave saturation of the current source converter by optimizing active power transmission during a fault and reducing the DC bus voltage amplitude, thereby achieving continuous and stable operation during the fault.

Description

Technical Field

[0001] The present invention relates to the technical field of stable external transmission application of new energy, and in particular to a design method of a sending-end station based on diode rectification and current source converter. Background Art

[0002] Modular multilevel converters (MMCs) offer excellent grid-connection voltage establishment and bidirectional power transmission capabilities, making them the mainstream choice for the Rectifier Station (RS) in offshore renewable energy transmission systems. However, the commonly used half-bridge MMCs contain a large number of switching devices and submodule capacitors, resulting in device cost, size, weight, and footprint far exceeding those of classic line-commutated converters (LCCs), significantly increasing the overall complexity of offshore AC system construction.

[0003] The diode rectifier (DR), a specialized form of LCC with a firing angle of zero, inherits the capacity, cost, and loss advantages of LCC for large-scale power transmission applications. It also eliminates the need for control and drive circuits and can be directly integrated into the step-up transformer. However, as an uncontrolled device, the DR cannot control the grid at the point of common coupling (PCC). When used in existing grid-connected wind farms, it requires additional starting cables, GPS broadcasting, reactive power compensation, harmonic suppression, and DC circuit breakers, significantly increasing overall transmission costs. Summary of the Invention

[0004] In order to address the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a sending station design method based on diode rectification and current source converter, which solves the problems of high cost, large amount of external equipment and complex control of the sending station in the offshore new energy transmission system.

[0005] The object of the present invention can be achieved by the following technical solution: a sending-end station design method based on diode rectification and current source converter, the method comprising the following steps:

[0006] Parameter design: select parameters that can ensure the system's steady-state operation and fault-tolerant operation;

[0007] Black start design: enables the new energy station to enter steady-state operation from shutdown;

[0008] DC fault ride-through design: prevents the system from experiencing overvoltage and overcurrent when a DC line short circuit occurs;

[0009] AC fault ride-through design: prevents the system from shutting down or disconnecting from the grid when a fault occurs on the AC line for a short period of time.

[0010] Preferably, the parameter design method is: perform a minimum cost search based on the power distribution constraint, the number constraint of diode rectifiers, the modulation ratio constraint of the current source converter, the DC voltage constraint of the current source converter, the steady-state active power constraint of the diode rectifier and the DC fault ride-through constraint of the current source converter, and further complete the design of other parameters based on the parameters obtained from the minimum cost search.

[0011] Preferably, the power allocation constraint is:

[0012]

[0013] Among them, k rpC and k rqC The output active and reactive proportions of the current source converter during rated operation, P rC , Q rC and S r is the output active and reactive power of the current source converter and the capacity of the sending station, n rD is the number of diode rectifiers, I rD is the amplitude of the AC current flowing into the diode rectifier, I r is the current amplitude of the sending station;

[0014] Based on the above power distribution, the number of diode rectifiers is constrained as follows:

[0015]

[0016] Among them, the number of diode rectifiers n rD , ce il is the ceiling rounding function.

[0017] Preferably, the modulation ratio constraint of the current source converter is:

[0018]

[0019] Among them, k rC is the transformer ratio of the current source converter, i dc is the DC bus current, L rC and C rC are the filter inductance and filter capacitance of the current source converter, ω N is the rated angular frequency, U r is the AC voltage amplitude at the sending station.

[0020] Preferably, the DC voltage constraint of the current source converter is:

[0021]

[0022] Among them, u rCdcis the DC voltage of the current source converter, M max is the maximum modulation ratio.

[0023] Preferably, the steady-state active power constraint of the diode rectification is:

[0024]

[0025] Among them, k rD and L rD is the transformer ratio and leakage inductance for diode rectification.

[0026] Preferably, the DC fault ride-through constraint of the current source converter is

[0027]

[0028] Preferably, the black start design process includes the following steps:

[0029] The receiving station controls the DC bus current to the rated value, and the sending station current source converter controls the PCC voltage to the rated value;

[0030] When the output power of the new energy station increases, the active power P of the input sending station is measured in real time. r ; Compare P r and diode rectifier rated power P rD , if P r ≥nP rD ,n=1,2,…,n rD , then close the AC circuit breaker of the nth diode rectifier until all diode rectifiers are put into the system;

[0031] When the DC bus voltage rises to the rated value, the receiving station control algorithm switches to rated DC bus voltage control.

[0032] Preferably, the DC fault ride-through design process includes:

[0033] When a DC fault is detected, an energy consumption device is connected to the AC side of the sending station so that all the active power input from the sending station flows into the energy consumption device.

[0034] Preferably, the AC fault ride-through design process includes:

[0035] Optimize the active power input to the sending station;

[0036] Adjust the DC bus voltage of the receiving station to satisfy the following equation

[0037]

[0038] A sending-end station based on diode rectification and current source converter comprises a structure in which a plurality of 12-pulse diode rectifications with the same parameters and a current source converter are connected in parallel on the AC side and in series on the DC side.

[0039] Beneficial effects of the present invention:

[0040] The present invention eliminates the need for starting cables, GPS broadcasting, reactive power compensation and harmonic suppression, and DC circuit breakers. It does not increase device voltage stress or incur additional costs when traversing DC faults or offshore AC faults. Compared with existing solutions, it has lower weight, volume, cost, and loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0042] Figure 1 It is the basic block diagram of the overall system of the present invention;

[0043] Figure 2 is a block diagram of a 6-pulse current source converter of the present invention;

[0044] Figure 3 It is a black start flow chart of the present invention. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0046] like Figure 1 As shown in the figure, the basic block diagram of the overall system mainly includes: new energy station, collection line, common collection point (PCC), AC circuit breaker, 12-pulse diode rectifier, current source converter, current limiting inductor, DC line, receiving station, and AC power grid.

[0047] Each new energy station is electrically connected to the corresponding collection line. All collection lines are electrically connected to the PCC. The PCC is electrically connected to the circuit breaker and 12-pulse rectifier. The AC side of the current source converter is electrically connected to the PCC, and the DC side is electrically connected to the 12-pulse diode rectifier. The 12-pulse diode rectifier is connected in series and electrically connected to the current-limiting inductor, DC line, receiving station, and AC grid.

[0048] The current source converter includes a three-winding transformer and two 6-pulse current source converters. The AC sides of the two 6-pulse current source converters are electrically connected to the two windings of the secondary side of the three-winding transformer respectively, and the DC sides of the two 6-pulse current source converters are connected in series. Figure 2 As shown, in a six-pulse current source converter, the upper-arm switching tubes, midpoint, and lower-arm switching tubes of each phase are electrically connected in sequence. The midpoint is electrically connected to the filter capacitor and filter inductor in sequence. The switching tubes used in the six-pulse current source converter are either IGBTs and diodes connected in series or IGCTs.

[0049] A method for designing a sending-end station based on diode rectification and current source converter, comprising:

[0050] Parameter design: select parameters that can ensure the system's steady-state operation and fault-tolerant operation;

[0051] Black start design: enables the new energy station to enter steady-state operation from shutdown;

[0052] DC fault ride-through design: prevents the system from experiencing overvoltage and overcurrent when a DC line short circuit occurs;

[0053] AC fault ride-through design: prevents the system from shutting down or disconnecting from the grid when a fault occurs on the AC line for a short period of time.

[0054] The specific method of parameter design is to perform a minimum cost search based on the power allocation constraints, the number constraints of diode rectifiers, the modulation ratio constraints of the current source converter, the DC voltage constraints of the current source converter, the steady-state active power constraints of the diode rectifier and the DC fault ride-through constraints of the current source converter, and further complete the design of other parameters based on the parameters obtained from the minimum cost search.

[0055] The power allocation constraint in parameter design is

[0056]

[0057] Among them, k rpC and k rqC The output active and reactive proportions of the current source converter during rated operation, P rC , Q rC and S r is the output active and reactive power of the current source converter and the capacity of the sending station, n rD is the number of diode rectifiers, I rD is the amplitude of the AC current flowing into the diode rectifier, I r is the current amplitude at the sending station.

[0058] Based on the above power distribution, the number of diode rectifiers in the parameter design is constrained as follows:

[0059]

[0060] Where ceil is the rounding up function.

[0061] The modulation ratio constraint of the current source converter in parameter design is

[0062]

[0063] Among them, k rC is the transformer ratio of the current source converter, i dc is the DC bus current, L rC and C rC are the filter inductance and filter capacitance of the current source converter, ω N is the rated angular frequency, U r is the AC voltage amplitude at the sending station.

[0064] The DC voltage constraint of the current source converter in parameter design is

[0065]

[0066] Among them, u rCdc is the DC voltage of the current source converter, M max is the maximum modulation ratio.

[0067] The steady-state active power constraint of the diode rectifier in parameter design is

[0068]

[0069] Among them, k rD and L rD is the transformer ratio and leakage inductance for diode rectification.

[0070] The DC fault ride-through constraint of the current source converter in parameter design is

[0071]

[0072] like Figure 3 As shown, the present invention provides a black start method, the specific steps are as follows:

[0073] S1. The receiving station controls the DC bus current to the rated value, and the sending station current source converter controls the PCC voltage to the rated value.

[0074] S2: When the output active power of the new energy station increases, the active power P of the input sending station is measured in real time r Compare Pr and diode rectifier rated power P rD , if P r ≥nP rD ,n=1,2,…,nrD , then close the AC circuit breaker of the nth diode rectifier until all diode rectifiers are put into the system.

[0075] S3: When the DC bus voltage rises to the rated value, the receiving station control algorithm switches to rated DC bus voltage control.

[0076] The present invention provides a DC fault ride-through method, specifically: when a DC fault is detected, an energy consumption device is connected to the AC side of a sending-end station so that all the active power input by the sending-end station flows into the energy consumption device.

[0077] The present invention provides a method for riding through an offshore AC fault.

[0078] S1. Optimize the active power input to the sending station according to the method shown in patent CN113098063B

[0079] S2. Adjust the DC bus voltage of the receiving station to satisfy the following equation

[0080]

[0081] A sending-end station based on diode rectification and current source converter comprises a structure in which a plurality of 12-pulse diode rectifications with the same parameters and a current source converter are connected in parallel on the AC side and in series on the DC side.

[0082] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0083] The above shows and describes the basic principles, main features and advantages of the present disclosure. Those skilled in the art should understand that the present disclosure is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present disclosure. Various changes and improvements may be made to the present disclosure without departing from the spirit and scope of the present disclosure, and such changes and improvements shall fall within the scope of the present disclosure.

Claims

1. A design method for a sending-end station based on diode rectification and current source converter, characterized in that: The method comprises the following steps: Parameter design: select parameters that can ensure the system's steady-state operation and fault-tolerant operation; Black start design: enables the new energy station to enter steady-state operation from shutdown; The process of black start design includes the following steps: The receiving station controls the DC bus current to the rated value, and the sending station current source converter controls the PCC voltage to the rated value; When the output power of the new energy station increases, the active power P of the input sending station is measured in real time. r ; Compare P r and diode rectifier rated power P rD , if P r ≥nP rD ,n=1,2,…,n rD , then close the AC circuit breaker of the nth diode rectifier until all diode rectifiers are put into the system; When the DC bus voltage rises to the rated value, the receiving station control algorithm switches to rated DC bus voltage control; DC fault ride-through design: prevents the system from experiencing overvoltage and overcurrent when a DC line short circuit occurs; The DC fault ride-through design process includes: When a DC fault is detected, an energy consumption device is connected to the AC side of the sending station so that all the input active power of the sending station flows into the energy consumption device. The AC fault ride-through design process includes: Optimize the active power input to the sending station; Adjust the DC bus voltage of the receiving station to satisfy the following equation AC fault ride-through design: prevents the system from shutting down or disconnecting from the grid when a fault occurs on the AC line for a short period of time.

2. The method for designing a sending-end station based on diode rectification and current source converter according to claim 1, characterized in that: The parameter design method is as follows: performing a minimum cost search based on power allocation constraints, number constraints of diode rectifiers, modulation ratio constraints of current source converters, DC voltage constraints of current source converters, steady-state active power constraints of diode rectifiers, and DC fault ride-through constraints of current source converters, and further completing other parameter designs based on the parameters obtained from the minimum cost search.

3. The design method of a sending-end station based on diode rectification and current source converter according to claim 2, characterized in that: The power allocation constraint is: Among them, k rpC and k rqC The output active and reactive proportions of the current source converter during rated operation, P rC , Q rC and S r is the output active and reactive power of the current source converter and the capacity of the sending station, n rD is the number of diodes rectified, I rD is the amplitude of the AC current flowing into the diode rectifier, I r is the current amplitude of the sending station; Based on the power distribution, the number of diode rectifiers is constrained as follows: Among them, the number of diode rectifiers n rD , ce il is the ceiling rounding function.

4. The method for designing a sending-end station based on diode rectification and current source converter according to claim 2, characterized in that: The modulation ratio constraint of the current source converter is: Among them, k rC is the transformer ratio of the current source converter, i dc is the DC bus current, L rC and C rC are the filter inductance and filter capacitance of the current source converter, ω N is the rated angular frequency, U r is the AC voltage amplitude at the sending station.

5. The method for designing a sending-end station based on diode rectification and current source converter according to claim 2, characterized in that: The DC voltage constraint of the current source converter is: Among them, u rCdc is the DC voltage of the current source converter, M max is the maximum modulation ratio.

6. The method for designing a sending-end station based on diode rectification and current source converter according to claim 2, characterized in that: The steady-state active power constraint of the diode rectification is: Among them, k rD and L rD Transformer ratio and leakage inductance for diode rectification.

7. The method for designing a sending-end station based on diode rectification and current source converter according to claim 2, characterized in that: The DC fault ride-through constraint of the current source converter is:

8. A sending-end station based on diode rectification and current source converter, adopting a sending-end station design method based on diode rectification and current source converter according to any one of claims 1 to 7, characterized in that: include: A structure in which multiple 12-pulse diode rectifiers with the same parameters and a current source converter are connected in parallel on the AC side and in series on the DC side.

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