Active and reactive power decoupling control method based on limited operation range

Abstract

The invention discloses an active and reactive power decoupling control method based on a limited operation range, and belongs to an LCC-HVDC decoupling control technology. Based on the constant current control of the rectifier and the constant voltage control of the inverter, the reactive power consumed by the converter can be adjusted under the condition that the active power of the rectifier and the inverter side is constant, and the adjustable range of the reactive power can be determined according to the method. The control method not only can provide a control basis for planning and stability analysis of the AC / DC system, but also provides a new idea for the converter to support the stability of the AC / DC hybrid system.

Description

Technical Field

[0001] The present invention belongs to LCC-HVDC decoupling control technology, and in particular relates to an active and reactive power decoupling control method based on a limited operating range. Background Art

[0002] With the widespread application of line-commutated converters based on high-voltage direct current systems (LCC-HVDC) in China, the converters consume a large amount of reactive power during normal operation. Currently, active and reactive power cannot be effectively decoupled in LCC-HVDC, and large-capacity AC filters are required in both rectifier and inverter stations. This is the fundamental reason that affects the safe and stable operation of AC and DC systems.

[0003] Currently, research on LCC-HVDC control primarily focuses on strategies for suppressing commutation failures. Building on this foundation, existing technologies such as "Transient overvoltage calculation method of HVDC sending-end system under DC bipolar blocking" and "Analytical Expression on Transient Overvoltage Peak Value of Converter Bus Caused by DC Faults" investigate the impact of commutation failures and DC blocking on AC system transient voltages. "Analytical Expression on Transient Overvoltage Peak Value of Converter Bus Caused by DC Faults" investigates strategies for restoring constant reactive power after commutation failures, but effective decoupling of active and reactive power remains unachieved. Based on this analysis, there is currently no research on decoupled control for LCC-HVDC.

[0004] To address these issues, this paper proposes a decoupled control method for active and reactive power within a limited operating range. This control method not only provides a control basis for AC / DC system planning and stability analysis, but also offers a new approach to converter-supported AC / DC hybrid system stability. Summary of the Invention

[0005] Purpose of the invention: The present invention aims to provide a method for decoupling active and reactive power based on a limited operating range, which can regulate the reactive power consumed by the converter under the condition that the active power on the rectifier and inverter sides is constant, and provides a new idea for the stability of the AC / DC hybrid system supported by the converter.

[0006] Technical solution: A decoupling control method for active and reactive power based on a limited operating range. Based on constant current control of the rectifier and constant voltage control of the inverter, this method can adjust the reactive power consumed by the converter while maintaining constant active power on the rectifier and inverter sides. The method can also determine the adjustable range of reactive power. Specifically, it includes the following control calculations:

[0007] Rectifier reactive power consumption Q d and the transmitted active power P d Expressed as:

[0008]

[0009] On the rectifier side, according to formula (1), the rectifier controls the DC current command value I dref,P for:

[0010]

[0011] When the reactive power consumption on the rectifier side Q dr =Q ref,r According to formula (1), the rectifier constant reactive power control DC current command value I dref,Q for:

[0012]

[0013] When the active power P d =P ref , Rectifier side reactive power consumption Q dr =Q ref,r , the rectifier sets the DC current command value I for active and reactive control dref,PQ for:

[0014]

[0015] On the inverter side, the DC voltage command value U is controlled based on the inverter active power. dref,P for:

[0016]

[0017] When the reactive power consumption on the inverter side Q di =Q ref,i, , the inverter constant reactive power control DC voltage command value U dref,Q for:

[0018]

[0019] When P d =P ref , Q di =Q ref,i , the inverter sets the active and reactive power control DC voltage command value U dref,PQ for:

[0020]

[0021] No-load DC voltage U on the rectifier and inverter sides dr0 and U di0 Expressed as:

[0022]

[0023] In the above formula, U d ,I d Represents DC voltage and DC current respectively, U d0 Indicates the no-load voltage, P ref ,Q ref Respectively represent the active power and reactive power command values, U dr Indicates the DC voltage on the rectifier side, Q ref , r Indicates the reactive power command value on the rectifier side, U dr0 Indicates the no-load DC voltage on the rectifier side, I di Indicates DC current, T r ,T i Indicates the transformation ratio of the converter transformer on the rectifier side and the inverter side, U Lr ,U Li Indicates the commutation bus voltage on the rectifier and inverter sides.

[0024] Furthermore, the method includes adopting a turn-off angle deviation control to avoid the inverter-side controller switching causing the turn-off angle to decrease and increase the risk of commutation failure. Its control characteristics are expressed as:

[0025] ΔU d =k(γ ref -γ) (9)

[0026] To avoid the DC current command value I dref and DC voltage command value U dref The effect of mutation was adjusted by stepwise adjustment I dref and U dref , the two satisfy the following relationship:

[0027]

[0028] Since the reactive power consumption Qd Depends on the active power P d , so when the active power P d When constant, the reactive power command value Q ref will be of limited scope;

[0029] When U dmin ≤U d ≤U dmax , I dref,max and I dref,min Expressed as:

[0030]

[0031] Therefore, the reactive power consumption Q d The range is calculated as:

[0032]

[0033] Based on formula (11) and formula (12), when P d When Q remains unchanged, d It can be controlled within a limited operating range, where n is the number of segments.

[0034] This method is based on the relationship between active power and reactive power. By adjusting the DC current in the rectifier and the DC voltage in the inverter, the reactive power consumed by the converter can be controlled without changing the active power.

[0035] Beneficial effects: The active and reactive power decoupling control method based on a limited operating range provided by the present invention can not only provide a control basis for the planning and stability analysis of AC / DC systems, but also provide a new idea for the stability of AC / DC hybrid systems supported by converters. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the control diagram of the rectifier side;

[0037] Figure 2 It is the inverter side control diagram (SIEMENS control strategy);

[0038] Figure 3 This is the active and reactive decoupling control strategy for the rectifier side and the inverter side provided by the present invention;

[0039] Figure 4 These are the simulation results of active power, reactive power, DC voltage, and DC current under different cases. DETAILED DESCRIPTION

[0040] For LCC-HVDC, HVDC control strategy plays an important role in ensuring stable operation of DC system. Currently, constant current (CC) control and constant active power (CAP) control are the most commonly used control strategies for rectifiers. The control diagram of the rectifier is shown in the figure below. Figure 1 As shown. Constant extinction angle (CEA) control and constant voltage (CV) control are widely used in inverters. Taking SIEMENS control strategy as an example, the control diagram of the inverter is as follows: Figure 2 shown.

[0041] Depend on Figure 1 It can be seen that the DC current command value on the rectifier side is given based on VDCOL and constant power control, but the reactive power consumption of the rectifier is not taken into account. Figure 2 ), constant voltage control provides a constant DC voltage command, but does not take into account the active power transmitted and reactive power consumed by the inverter. Currently, existing control strategies cannot achieve the decoupling of active and reactive power in LCC-HVDC.

[0042] Combined with the technical solution provided by the present invention, the active power and reactive power decoupling control strategy (ARPDC) is as follows Figure 3 shown. Figure 3 The parameters can be found in Table 1.

[0043] Table 1. Comparison table of main symbols

[0044] <![CDATA[P ref ,Q ref ]]> Active power and reactive power command values <![CDATA[U d ,I d ]]> DC voltage, DC current <![CDATA[U dr ,I dr ]]> Rectifier side DC voltage and DC current <![CDATA[U di ,I di ]]> Inverter side DC voltage and DC current <![CDATA[I dref,V ]]> VDCOL output DC current command value <![CDATA[I dref,P ,I dref,Q ]]> Constant active power and constant reactive power control DC current command value <![CDATA[U dref,P ,IN dref,Q ]]> Constant active power and constant reactive power control DC voltage command value <![CDATA[Q dr ,Q di ]]> Reactive power consumption on the rectifier and inverter sides <![CDATA[γ,γ ref ]]> Shut-off angle and shut-off angle command value <![CDATA[U dr0 ,IN di0 ]]> No-load DC voltage on the rectifier and inverter sides N Number of six-pulse converters <![CDATA[T r ,T i ]]> Converter transformer ratio on the rectifier and inverter sides <![CDATA[U Lr ,IN Li ]]> Rectifier side and inverter side commutation bus voltage

[0045] Depend on Figure 3 It can be seen that S in the rectifier r1 , S r2 and S r3 , S in the inverter i1 , S i2 and S i3 Different control functions are determined for different S. To avoid the inverter-side controller switching causing the turn-off angle to decrease and increase the risk of commutation failure, the inverter adopts turn-off angle deviation control.

[0046] Based on the CIGREHVDC standard test model parameters, the SIEMENS control strategy was established in PSCAD, and based on this, the ARPDC was established. For the simulation model, under normal operating conditions, P dN =1000MW, U drN=500kV, I dN =2kA, U dmax =1.1pu,U dmin =0.95pu. When P ref =1000MW, according to equations (11) and (12), on the rectifier side, Q ref,r The operating range is 311MVar≤Q ref,r ≤686MVar. On the inverter side, Q ref,i The operating range is 235MVar≤Q ref,i ≤644MVar. For P ref =500MW, Q ref,r and Q ref,i The ranges are [156,343] and [117,322].

[0047] The example is as follows:

[0048] Case A: Q ref,r =400MVar;

[0049] Case B: Q ref,r =600MVar;

[0050] Case C: Q ref,i =300MVar; Case D: Q ref,i =500MVar.

[0051] For all cases, P ref =1000MW, the inverter control switches to ICARP at 3s, and the rectifier control switches to RCARP at 3.2s.

[0052] Depend on Figure 4 It can be seen that for all cases, under ARPDC, the active power can be effectively controlled at 1 pu, but the reactive power consumed by the rectifier and inverter may be different. For Case A, when Q ref,r =400MVar, Q dr The power is controlled at 375 MVar. Although there are errors in all cases, it also proves the effectiveness of active and reactive power decoupling control. It also proves that reactive power can be decoupled from active power in LCC-HVDC system.

[0053] Based on constant rectifier current control and inverter voltage control, this paper proposes a decoupled control method for active and reactive power within a limited operating range. Based on an analysis of the relationship between active and reactive power, by adjusting the DC current in the rectifier and the DC voltage in the inverter, the reactive power consumed by the converter can be controlled while maintaining constant active power. Simulation results demonstrate that the proposed control strategy effectively decouples active and reactive power.

Claims

1. A method for decoupling active and reactive power based on a limited operating range, characterized in that: Based on the constant current control of the rectifier and the constant voltage control of the inverter, this method can adjust the reactive power consumed by the converter under the condition that the active power on the rectifier and inverter sides is constant. The adjustable range of reactive power can be determined according to this method. Specifically, the control calculation includes the following: Rectifier reactive power consumption Q d and the transmitted active power P d Expressed as: On the rectifier side, according to formula (1), the rectifier controls the DC current command value I dref,P for: When the reactive power consumption on the rectifier side Q dr =Q ref,r According to formula (1), the rectifier constant reactive power control DC current command value I dref,Q for: When the active power P d =P ref , Rectifier side reactive power consumption Q dr =Q ref,r , the rectifier sets the DC current command value I for active and reactive control dref,PQ for: On the inverter side, the DC voltage command value U is controlled based on the inverter active power. dref,P for: When the reactive power consumption on the inverter side Q di =Q ref,i, , the inverter constant reactive power control DC voltage command value U dref,Q for: When P d =P ref , Q di =Q ref,i , the inverter sets the active and reactive power control DC voltage command value U dref,PQ for: No-load DC voltage U on the rectifier and inverter sides dr0 and U di0 Expressed as: In the above formula, U d ,I d Represents DC voltage and DC current respectively, U d0 Indicates the no-load voltage, P ref ,Q ref Respectively represent the active power and reactive power command values, U dr Indicates the DC voltage on the rectifier side, Q ref,r Indicates the reactive power command value on the rectifier side, U dr0 Indicates the no-load DC voltage on the rectifier side, I di Indicates DC current, T r ,T i Indicates the transformation ratio of the converter transformer on the rectifier side and the inverter side, U Lr ,U Li Indicates the commutation bus voltage on the rectifier and inverter sides.

2. The method for decoupling active and reactive power based on a limited operating range according to claim 1, characterized in that: This method includes using turn-off angle deviation control to avoid the inverter-side controller switching causing the turn-off angle to decrease and increase the risk of commutation failure. Its control characteristics are expressed as: D.U. d =k(γ ref -c) (9) To avoid the DC current command value I dref and DC voltage command value U dref The effect of mutation was adjusted by stepwise adjustment I dref and U dref , the two satisfy the following relationship: Since the reactive power consumption Q d Depends on the active power P d , so when the active power P d When constant, the reactive power command value Q ref will be of limited scope; WhenU dmin ≤U d ≤U dmax , I dref,max and I dref,min Expressed as: Therefore, the reactive power consumption Q d The range is calculated as: Based on formula (11) and formula (12), when P d When Q remains unchanged, d It can be controlled within a limited operating range, where n is the number of segments.

3. The method for decoupling active and reactive power based on a limited operating range according to claim 1, characterized in that: This method is based on the relationship between active power and reactive power. By adjusting the DC current in the rectifier and the DC voltage in the inverter, the reactive power consumed by the converter can be controlled without changing the active power.

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