A method and device for comprehensive optimization control of three-phase imbalance and light and heavy loads in a multi-station interconnected power distribution system

Abstract

The present invention discloses a method for comprehensive optimization control of three-phase imbalance and light and heavy loads for a multi-station interconnected power distribution system, including: obtaining the actual values ​​of the three-phase voltage and current of the grid-connected points of the AC / DC converters of each station area, and obtaining a three-phase voltage set and a three-phase current set; obtaining the active power shortage of each station area and the reactive power shortage of each station area according to the three-phase voltage set; obtaining a first data set according to the active power shortage of each station area combined with primary unbalanced power control and secondary load-balancing operation control; obtaining a second data set according to the reactive power shortage of each station area and the first data set; obtaining a third data set according to the three-phase current set and the second data set; obtaining the switch signals of the four bridge arms of the AC / DC converters of each station area according to the third data set, and controlling the AC / DC converters of each station area according to the switch signals to achieve comprehensive management of three-phase imbalance and light and heavy loads. A method for comprehensive optimization control of three-phase imbalance and light and heavy loads for a multi-station interconnected power distribution system is also disclosed.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution network, and in particular to a method and device for comprehensive optimization control of three-phase imbalance and light and heavy loads for a multi-station interconnected power distribution system. Background Art

[0002] Distributed power sources, mainly distributed photovoltaics, are entering a stage of rapid development. With the widespread promotion of low-carbon, zero-carbon, and negative-carbon technologies, distribution networks, especially low-voltage distribution networks, as the "last mile" of power supply, play a key role in ensuring the balance of power supply and demand and promoting the efficient use of new energy. The access of a large number of distributed power sources has brought more uncertainty and randomness to the low-voltage distribution network. At the same time, the disordered and mixed access of single-phase and three-phase loads has further aggravated the three-phase imbalance problem and led to frequent light and heavy load operations in the substation area. This not only threatens the power supply quality and operating efficiency, but also significantly increases the risks of grid stability and economic operation.

[0003] The solutions to the three-phase imbalance problem mainly include capacitor switching, reactive power compensation and phase sequence reorganization. Switching capacitors can achieve reactive power and slight imbalance compensation, but the adjustment accuracy is limited; reactive power compensation devices can eliminate negative-sequence and zero-sequence currents, but the cost is high; reorganization of phase sequence improves balance by dynamically adjusting the load phase, but the technology is complex and the investment and maintenance costs are expensive. In terms of managing light and heavy load operation in substations, load transfer methods based on the interconnection of multiple substations can effectively alleviate the problem of light and heavy loads on feeders. However, how to achieve comprehensive management of three-phase imbalance and light and heavy load problems in substations is currently in urgent need of resolution.

[0004] Therefore, a new technical solution is urgently needed to solve the technical problem of how to comprehensively manage three-phase imbalance and light and heavy load problems in transformer areas. Summary of the invention

[0005] The present invention provides a method and device for comprehensive optimization control of three-phase imbalance and light and heavy loads in a multi-station interconnected power distribution system, which is used to solve the technical problem of how to comprehensively manage the three-phase imbalance and light and heavy load problems in the stations.

[0006] To achieve the above-mentioned object, the present invention provides a three-phase unbalanced and light and heavy load comprehensive optimization control method for a multi-station interconnected power distribution system, the system includes a fixed DC bus voltage control station area and at least one fixed active and reactive power control station area; the method includes:

[0007] The actual values ​​of the three-phase voltage and current of the grid-connected points of the AC / DC converters in each substation are obtained to obtain a three-phase voltage set and a three-phase current set; the active power deficit and reactive power deficit of each substation are obtained according to the three-phase voltage set.

[0008] The first data set is obtained according to the active power shortage of each substation in combination with the primary unbalanced power control and the secondary load-balancing operation control; the first data set includes the active power reference input value of each phase of the AC / DC converter of each substation.

[0009] The second data set is obtained according to the reactive power shortage of each substation and the first data set; the second data set includes the three-phase current management reference value of each substation.

[0010] The third data set is obtained according to the three-phase current set and the second data set; the third data set includes the zero-sequence voltage and output voltage of the AC / DC converter in each substation area. Positive and negative sequence components in the coordinate system.

[0011] The switching signals of the four bridge arms of the AC / DC converter in each substation are obtained according to the third data set, and the AC / DC converter in each substation is controlled according to the switching signals to achieve comprehensive management of three-phase imbalance and light and heavy loads.

[0012] Preferably, the active power shortage of each substation area includes:

[0013] The active power shortage of each substation is obtained based on the three-phase voltage set, including:

[0014] Decompose the actual value of the three-phase voltage according to the symmetrical component method to obtain Positive sequence voltage in the coordinate system and ; The positive sequence voltage and From still The coordinate system is transformed back to the three-phase coordinate system to obtain the voltage reference value of each phase and ; The actual value of the three-phase voltage is expressed as and ;Will and and and and The phase angle deviations are expressed as and .

[0015] Will and After PI adjustment, the initial reference command value of active power of each phase can be obtained, that is, the active power shortage , ; By solving for each substation, the active power shortage of each substation can be obtained.

[0016] Preferably, the reactive power shortage of each substation area includes:

[0017] The reactive power shortage of each substation is obtained based on the three-phase voltage set, including:

[0018] Calculate the effective value of each phase of the three-phase voltage actual value With each phase voltage reference value The voltage RMS deviation.

[0019] The voltage effective value deviation is adjusted by PI to obtain the Phase reactive power reference command value, i.e. reactive power shortage , ; By solving for each substation, the reactive power shortage of each substation can be obtained.

[0020] Preferably, the first data set obtained according to the active power shortage of each substation combined with the primary unbalanced power control and the secondary load balancing operation control includes:

[0021] The fourth data set is obtained based on the primary unbalanced power control according to the active power shortage of each substation; the fourth data set includes the active power reference instruction value of each phase for the AC / DC converter of each substation to control the three-phase imbalance.

[0022] The first data set is obtained based on the second load balancing operation control according to the fourth data set.

[0023] Preferably, the fourth data set obtained based on the primary unbalanced power control according to the active power shortage of each substation area includes:

[0024] Get the real-time power flowing from the DC side to the AC side ; According to the active power shortage Based on the primary unbalanced power control, the active power reference command value of each phase of the AC / DC converter in the substation area is obtained to control the three-phase imbalance , , which can be expressed as:

[0025] in, express Phase active power shortage; express Phase active power shortage; express Phase active power shortage; by solving for each substation, the fourth data set can be obtained.

[0026] Preferably, obtaining the first data set based on the secondary load balancing operation control according to the fourth data set includes:

[0027] Secondary load balancing operation control is based on the active power reference command value Get the active power reference input value of each phase of the AC / DC converter in the substation area Assuming the area The active power reference command value is , the active power reference input value is The actual load is , the transformer capacity is Assuming that there is a total Each area is interconnected, ; If the operation status of the substation includes the optimal economic operation status, light load operation status and heavy load operation status, then the active power reference input value is exist:

[0028] Scenario 1: All stations are in the same operating state; It can be expressed as: ;

[0029] Scenario 2: Each area is in the best economic operation state. The substation is in light load operation state, but at this time The load power required for each transformer in the substation to increase to 25% load rate is less than or equal to The load power required to be transferred when the load factor of each area drops to 25%;

[0030] In the second scenario, if the In the best economic operation state, It can be expressed as: ;

[0031] In the second scenario, if the In light load operation, It can be expressed as: ;

[0032] Scenario 3: Each area is in the best economic operation state. The substation is in light load operation state, but at this time The load power required for the transformer in each area to increase to 25% load factor is greater than The load power required to be transferred when the load factor of each area drops to 25%;

[0033] In case 3, if the Taiwan area In the best economic operation state, It can be expressed as: ;

[0034] In case 3, if the Taiwan area In light load operation, It can be expressed as: ;

[0035] Scenario 4: Each area is in the best economic operation state. The area is in heavy load operation, but at this time The load power required to be transferred when the load factor of each transformer in the substation is reduced to 75% is less than or equal to The load power required to increase the load factor of each area to 75%;

[0036] In case 4, if the Taiwan area In the best economic operation state, It can be expressed as: ;

[0037] In case 4, if the Taiwan area In heavy load operation, It can be expressed as: ;

[0038] Scenario 5: Each area is in the best economic operation state. The area is in heavy load operation, but at this time The load power required to transfer from the transformer in each area to 75% load factor is greater than The load power required to increase the load factor of each area to 75%;

[0039] In case 5, if the Taiwan area In the best economic operation state, It can be expressed as: ;

[0040] In case 5, if the Taiwan area In heavy load operation, It can be expressed as: ;

[0041] Scenario 6: Each area is in light load operation state. Each area is in heavy load operation;

[0042] In case 6, if the area In light load operation, It can be expressed as: ;

[0043] In case 6, if the Taiwan area In heavy load operation, It can be expressed as: ;

[0044] The first data set can be obtained by solving each station area.

[0045] Preferably, obtaining the second data set according to the reactive power shortage of each substation area and the first data set includes:

[0046] Three-phase current management reference value in the second data set It can be expressed as:

[0047] ; ;

[0048] in, , Indicates The reactive power reference command value of each phase, i.e., the reactive power shortage; Indicates the AC / DC converter grid-connected i The effective value of the phase voltage; Indicates the phase of the positive sequence component of the grid fundamental frequency output by the phase-locked loop in real time; ; Indicates The angle between the phase voltage and current.

[0049] The second data set can be obtained by solving each station area.

[0050] Preferably, obtaining the third data set according to the three-phase current set and the second data set includes:

[0051] The Clark transformation is used to transform the actual value of the three-phase current in the three-phase current set and the three-phase current management reference value in the second data set to the stationary Coordinate system, Clark transformation can be expressed as:

[0052] ;get Positive sequence reference current in the coordinate system and , negative sequence reference current and , zero sequence reference current , Positive sequence actual current and and negative sequence actual current and ; and obtain the actual zero-sequence current ;

[0053] Will The positive sequence reference current, negative sequence reference current, positive sequence actual current and negative sequence actual current in the coordinate system are from the static Coordinate transformation to rotation Coordinate system, the expression of transformation can be expressed as: ;

[0054] in, Indicates the grid angular frequency; Indicates time; represents the rotation angle;

[0055] Rotation angle when positive sequence reference current and positive sequence actual current are transformed The phase of the positive sequence component of the grid fundamental frequency output by the phase-locked loop in real time ,get and .

[0056] Rotation angle when negative sequence reference current and negative sequence actual current are transformed for ,get and .

[0057] Perform current inner loop control to obtain the output voltage of the AC / DC converter in the station area. Positive and negative sequence components in the coordinate system:

[0058] If the AC / DC converter in the substation is controlled by a fixed DC bus voltage, the output voltage of the AC / DC converter is The positive sequence component in the coordinate system is and , the negative sequence component is and , which can be expressed as:

[0059] ; ;

[0060] ;

[0061] ;

[0062] If the AC / DC converter in the substation is controlled by fixed active and reactive power, the output voltage of the AC / DC converter is dq The positive sequence component in the coordinate system is and , the negative sequence component is and , which can be expressed as:

[0063] ; ; ; ;

[0064] in, and Indicates the PI parameters of the PI regulators of the first bridge arm, the second bridge arm and the third bridge arm of the AC / DC converter; represents a complex frequency domain variable; and Indicates the PI parameters of the DC bus voltage PI regulator; Indicates the DC bus voltage value; Indicates the DC bus voltage reference value; Indicates the inductance value of the LC filter in the AC / DC converter.

[0065] The output voltage of the fourth bridge arm of the AC / DC converter, i.e. the zero-sequence voltage It can be expressed as:

[0066] ;in, Represents the parameters of the fourth bridge arm P regulator of the AC / DC converter.

[0067] The third data set can be obtained by solving the problem for each station area.

[0068] Preferably, the switching signals of the four bridge arms of the AC / DC converter in each area are obtained according to the third data set, including:

[0069] According to the AC / DC converter output voltage The positive sequence component and the negative sequence component in the coordinate system are respectively subjected to inverse Park transformation and then added to obtain the three-phase voltage reference value in the abc coordinate system.

[0070] The three-phase voltage reference value and the zero-sequence voltage under the abc coordinates are pulse-width modulated to obtain the switching signals of the first three bridge arms and the switching signal of the fourth bridge arm of the AC / DC converter respectively.

[0071] The present invention also provides a three-phase unbalanced and light and heavy load comprehensive optimization control device for a multi-station interconnected distribution system, which is used for the method of the present invention. The device includes a first module, a second module, a third module, a fourth module, a fifth module and a sixth module.

[0072] The first module is used to obtain the three-phase voltage and current of the grid-connected point of the AC / DC converter in each substation, and obtain the three-phase voltage set and the three-phase current set.

[0073] The second module is used to obtain the active power shortage and reactive power shortage of each substation area according to the three-phase voltage set.

[0074] The third module is used to obtain a first data set based on the active power shortage of each substation combined with primary unbalanced power control and secondary load balancing operation control; the first data set includes active power reference input values ​​of each phase of the AC / DC converter of each substation.

[0075] The fourth module is used to obtain a second data set based on the reactive power shortage of each substation and the first data set; the second data set includes a three-phase current management reference value of each substation.

[0076] The fifth module is used to obtain a third data set according to the three-phase current set and the second data set; the third data set includes the zero-sequence voltage and output voltage of the AC / DC converter in each substation area. Positive and negative sequence components in the coordinate system.

[0077] The sixth module is used to obtain the switching signals of the four bridge arms of the AC / DC converter in each substation according to the third data set, and control the AC / DC converter in each substation according to the switching signals to achieve comprehensive management of three-phase imbalance and light and heavy loads.

[0078] The present invention has the following beneficial effects:

[0079] The three-phase unbalanced and light and heavy load comprehensive optimization control method for the interconnected distribution system of multiple substations of the present invention is based on the power sensing method of positive and negative sequence separation. It can realize the three-phase active sensing of the unbalanced power of each substation without measuring the unbalanced operating state of the AC load side of the substation; based on the primary unbalanced power control and the secondary load-balancing operation control, it provides a power reference value for the unbalanced power control, reduces the measurement error of the unbalanced power and reduces the device cost. Without adding additional devices, the existing AC / DC converters of each substation are controlled according to the method of the present invention, so as to actively realize the efficient comprehensive optimization of the three-phase unbalanced and light and heavy load problems of multiple substations, and effectively alleviate the high and low voltage problems of the substations. The method of the present invention can realize the real-time bidirectional power flow between two or more low-voltage substations, and at the same time, by stabilizing the DC bus voltage, realize the efficient access of DC sources, loads and storage, and further enhance the flexibility and dynamic optimization capability of power flow in multiple substations.

[0080] The three-phase unbalanced and light-and-heavy load comprehensive optimization control device for a multi-station interconnected power distribution system of the present invention is used in the method of the present invention and has the same beneficial effects as the method of the present invention.

[0081] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0083] Figure 1 It is a schematic diagram of a multi-area interconnected power distribution system according to a preferred embodiment of the present invention.

[0084] Figure 2 It is a schematic diagram of a method flow of a preferred embodiment of the present invention.

[0085] Figure 3It is a schematic diagram of calculating the initial reference command value of active power in a preferred embodiment of the present invention.

[0086] Figure 4 It is a schematic diagram of calculating the reactive power reference command value according to a preferred embodiment of the present invention.

[0087] Figure 5 It is a schematic diagram of the control principle of the AC / DC converter in the constant DC bus voltage control console area of ​​the preferred embodiment of the present invention.

[0088] Figure 6 It is a schematic diagram of the control principle of the AC / DC converter in the fixed active and reactive power control console area of ​​the preferred embodiment of the present invention.

[0089] Figure 7 It is a schematic diagram of a two-area interconnected power distribution system according to a preferred embodiment of the present invention.

[0090] Figure 8 It is a voltage waveform diagram of the grid connection point of the AC / DC converter in front area 1 before using the method of the present invention in a preferred embodiment of the present invention.

[0091] Fig. 9 It is a voltage waveform diagram of the grid connection point of the AC / DC converter in front area 2 before using the method of the present invention in a preferred embodiment of the present invention.

[0092] Fig.10 It is a voltage waveform diagram of the grid connection point of the AC / DC converter in the back-end area 1 after using the method of the present invention in a preferred embodiment of the present invention.

[0093] Fig.11 It is a voltage waveform diagram of the grid connection point of the AC / DC converter in the back-end area 2 after using the method of the present invention in a preferred embodiment of the present invention.

[0094] Fig.12 It is a schematic diagram of the grid-side output active power of the substation area 1 and the substation area 2 according to the preferred embodiment of the present invention.

[0095] Fig.13 It is a voltage waveform diagram of the grid connection point of the AC / DC converter in the station area 1 according to the preferred embodiment of the present invention.

[0096] Fig.14 It is a schematic diagram of the three-phase output active power of the AC / DC converter in the station area 1 according to the preferred embodiment of the present invention.

[0097] Fig.15 It is a voltage waveform diagram of the grid connection point of the AC / DC converter in the station area 2 according to the preferred embodiment of the present invention.

[0098] Fig.16 It is a schematic diagram of the three-phase output active power of the AC / DC converter in the station area 2 according to the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0099] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0100] See also Figure 1 In a preferred embodiment of the present invention, a multi-area interconnected power distribution system includes:

[0101] The primary side of each transformer in each substation is connected to the high-voltage AC bus, and the secondary side is connected to the low-voltage AC bus. The AC load and AC / DC converter in the substation are connected to the low-voltage AC bus. The AC / DC converter in each substation is the interface for interconnection between substations. The AC / DC converter consists of a full-bridge inverter with three phases and four bridge arms (the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm) and an LC filter. The conduction circuit is controlled by two IGBT switches in each bridge arm. The low-voltage DC distribution network composed of photovoltaic, energy storage and DC loads is interconnected with the AC / DC converter in the substation through the DC bus, thereby interconnecting multiple substations.

[0102] See also Figure 2 In a preferred embodiment of the present invention, a three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-station interconnected power distribution system is provided, comprising:

[0103] S1. Obtain the actual values ​​of the three-phase voltage and current of the grid connection point of the AC / DC converter (AC to DC converter) of each substation to obtain a three-phase voltage set and a three-phase current set; obtain the active power deficit and reactive power deficit of each substation based on the three-phase voltage set.

[0104] In a preferred embodiment of the present invention, the active power shortage of each substation area includes:

[0105] The active power shortage of each substation is obtained based on the three-phase voltage set, including:

[0106] The three-phase voltage The phase of the positive sequence component of the fundamental frequency is obtained by using a phase-locked loop .

[0107] Decompose the actual value of the three-phase voltage according to the symmetrical component method to obtain Positive sequence voltage in the coordinate system and ; The positive sequence voltage and From still The coordinate system is transformed back to the three-phase coordinate system to obtain the voltage reference value of each phase and ; The actual value of the three-phase voltage is expressed as and ;Will and and and and Phase angle deviation Respectively expressed as and .

[0108] See also Figure 3 ,Will and After PI adjustment, the initial reference command value of active power of each phase can be obtained, that is, the active power shortage , ; By solving for each substation, the active power shortage of each substation can be obtained.

[0109] In a preferred embodiment of the present invention, the reactive power shortage of each substation area includes:

[0110] The reactive power shortage of each substation is obtained based on the three-phase voltage set, including:

[0111] See also Figure 4 , calculate the effective value of each phase of the three-phase voltage actual value With each phase voltage reference value The voltage effective value deviation is obtained by adjusting the voltage effective value deviation through PI. i Phase reactive power reference command value, i.e. reactive power shortage , ; By solving for each substation, the reactive power shortage of each substation can be obtained. The value is usually 220V.

[0112] S2. A first data set is obtained based on the active power shortage of each substation combined with primary unbalanced power control and secondary load-balancing operation control; the first data set includes active power reference input values ​​of each phase of the AC / DC converter of each substation. S2 specifically includes:

[0113] In a preferred embodiment of the present invention, a fourth data set is obtained based on primary unbalanced power control according to the active power shortage of each substation; the fourth data set includes active power reference command values ​​of each phase of the AC / DC converter of each substation for controlling three-phase imbalance.

[0114] The first data set is obtained based on the second load balancing operation control according to the fourth data set.

[0115] In a preferred embodiment of the present invention, the fourth data set obtained based on the primary unbalanced power control according to the active power shortage of each substation includes:

[0116] Get the real-time power flowing from the DC side to the AC side ; According to the active power shortage Based on the primary unbalanced power control, the active power reference command value of each phase of the AC / DC converter in the substation area is obtained to control the three-phase imbalance. , , which can be expressed as:

[0117] ; ; ;in, express Phase active power shortage; express Phase active power shortage; express Phase active power shortage; by solving for each substation, the fourth data set can be obtained.

[0118] In a preferred embodiment of the present invention, obtaining the first data set based on the second load balancing operation control according to the fourth data set includes:

[0119] Secondary load balancing operation control is based on the active power reference command value Get the active power reference input value of each phase of the AC / DC converter in the substation area Assuming the area The active power reference command value is , the active power reference input value is The actual load is , the transformer capacity is Assuming that there is a total Each area is interconnected, ; If the operation status of the substation includes the optimal economic operation status, light load operation status and heavy load operation status, then the active power reference input value is exist:

[0120] Scenario 1: All stations are in the same operating state; It can be expressed as: ;

[0121] Scenario 2: Each area is in the best economic operation state. The substation is in light load operation state, but at this time The load power required for each transformer in the substation to increase to 25% load rate is less than or equal to The load power required to be transferred when the load factor of each area drops to 25%;

[0122] In case 2, if the In the best economic operation state, It can be expressed as: ;

[0123] In case 2, if the In light load operation, It can be expressed as: ;

[0124] Scenario 3: Each area is in the best economic operation state. The substation is in light load operation state, but at this time The load power required for the transformer in each area to increase to 25% load factor is greater than The load power required to be transferred when the load factor of each area drops to 25%;

[0125] In case 3, if the Taiwan area In the best economic operation state, It can be expressed as: ;

[0126] In case 3, if the Taiwan area In light load operation, It can be expressed as: ;

[0127] Scenario 4: Each area is in the best economic operation state. The area is in heavy load operation, but at this time The load power required to be transferred when the load factor of each transformer in the substation is reduced to 75% is less than or equal to The load power required to increase the load factor of each area to 75%;

[0128] In case 4, if the Taiwan area In the best economic operation state, It can be expressed as: ;

[0129] In case 4, if the Taiwan area In heavy load operation, It can be expressed as: ;

[0130] Scenario 5: Each area is in the best economic operation state. The area is in heavy load operation, but at this time The load power required to transfer from the transformer in each area to 75% load factor is greater than The load power required to increase the load factor of each area to 75%;

[0131] In case 5, if the Taiwan area In the best economic operation state, It can be expressed as: ;

[0132] In case 5, if the Taiwan area In heavy load operation, It can be expressed as: ;

[0133] Scenario 6: Each area is in light load operation state. Each area is in heavy load operation;

[0134] In case 6, if the Taiwan area In light load operation, It can be expressed as: ;

[0135] In case 6, if the Taiwan area In heavy load operation, It can be expressed as: ;

[0136] The first data set can be obtained by solving each station area.

[0137] S3, obtaining a second data set based on the reactive power shortage of each substation and the first data set; the second data set includes the three-phase current management reference value of each substation. S3 specifically includes:

[0138] Three-phase current management reference value in the second data set It can be expressed as:

[0139] ; in, , Indicates The reactive power reference command value of each phase, i.e., the reactive power shortage; Indicates the AC / DC converter grid-connected i The effective value of the phase voltage; Indicates the phase of the positive sequence component of the grid fundamental frequency output by the phase-locked loop in real time; ; Indicates The angle between the phase voltage and current.

[0140] The second data set can be obtained by solving each station area.

[0141] S4, obtaining a third data set according to the three-phase current set and the second data set; the third data set includes the zero-sequence voltage and output voltage of the AC / DC converter in each substation area The positive and negative sequence components in the coordinate system. S4 specifically includes:

[0142] The Clark transformation is used to transform the actual value of the three-phase current in the three-phase current set and the three-phase current management reference value in the second data set to the stationary Coordinate system, Clark transformation can be expressed as:

[0143] ;get Positive sequence reference current in the coordinate system and , negative sequence reference current and , zero sequence reference current , Positive sequence actual current and and negative sequence actual current and ; and obtain the actual zero-sequence current .

[0144] Will The positive sequence reference current, negative sequence reference current, positive sequence actual current and negative sequence actual current in the coordinate system are from the static Coordinate transformation to rotation Coordinate system, the expression of transformation can be expressed as: ;

[0145] in, Indicates the grid angular frequency; Indicates time; represents the rotation angle;

[0146] Rotation angle when positive sequence reference current and positive sequence actual current are transformed The phase of the positive sequence component of the grid fundamental frequency output by the phase-locked loop in real time ,get and .

[0147] Rotation angle when negative sequence reference current and negative sequence actual current are transformed for ,get and .

[0148] Perform current inner loop control to obtain the output voltage of the AC / DC converter in the station area. Positive and negative sequence components in the coordinate system:

[0149] See also Figure 5 If the AC / DC converter in the substation is controlled by a fixed DC bus voltage, the output voltage of the AC / DC converter is The positive sequence component in the coordinate system is and , the negative sequence component is and , which can be expressed as:

[0150] ; ;

[0151] ;

[0152] ;

[0153] See also Figure 6 If the AC / DC converter in the substation is controlled by fixed active and reactive power, the output voltage of the AC / DC converter is The positive sequence component in the coordinate system is and , the negative sequence component is and , which can be expressed as:

[0154] ; ; ; ;

[0155] in, and Indicates the PI parameters of the PI regulators of the first bridge arm, the second bridge arm and the third bridge arm of the AC / DC converter; represents a complex frequency domain variable; and Indicates the PI parameters of the DC bus voltage PI regulator; Indicates the DC bus voltage value; Indicates the DC bus voltage reference value; Indicates the inductance value of the LC filter in the AC / DC converter.

[0156] See also Figures 5 and 6 , the output voltage of the fourth bridge arm of the AC / DC converter, that is, the zero-sequence voltage It can be expressed as:

[0157] ;in, Represents the parameters of the fourth bridge arm P regulator of the AC / DC converter.

[0158] The third data set can be obtained by solving the problem for each station area.

[0159] S5. Obtain the switch signals of the four bridge arms of the AC / DC converter in each area according to the third data set, and control the AC / DC converter in each area according to the switch signals to achieve comprehensive management of three-phase imbalance and light and heavy loads. S5 specifically includes:

[0160] According to the AC / DC converter output voltage The positive sequence component and the negative sequence component in the coordinate system are respectively subjected to inverse Park transformation and then added to obtain the three-phase voltage reference value in the abc coordinate system.

[0161] The three-phase voltage reference value and the zero-sequence voltage under the abc coordinates are pulse-width modulated to obtain the switching signals S1-S6 of the first three bridge arms of the AC / DC converter and the switching signals S7-S8 of the fourth bridge arm.

[0162] The three-phase unbalanced and light and heavy load comprehensive optimization control method for the interconnected distribution system of multiple substations of the present invention is based on the power sensing method of positive and negative sequence separation. It can realize the three-phase active sensing of the unbalanced power of each substation without measuring the unbalanced operating state of the AC load side of the substation; based on the primary unbalanced power control and the secondary load-balancing operation control, it provides a power reference value for the unbalanced power control, reduces the measurement error of the unbalanced power and reduces the device cost. Without adding additional devices, the existing AC / DC converters of each substation are controlled according to the method of the present invention, so as to actively realize the efficient comprehensive optimization of the three-phase unbalanced and light and heavy load problems of multiple substations, and effectively alleviate the high and low voltage problems of the substations. The method of the present invention can realize the real-time bidirectional power flow between two or more low-voltage substations, and at the same time, by stabilizing the DC bus voltage, realize the efficient access of DC sources, loads and storage, and further enhance the flexibility and dynamic optimization capability of power flow in multiple substations.

[0163] In a preferred embodiment of the present invention, a three-phase unbalanced and light-heavy load integrated optimization control device for a multi-station interconnected power distribution system is also provided, which is used in the method of the present invention, and the device includes a first module, a second module, a third module, a fourth module, a fifth module and a sixth module;

[0164] The first module is used to obtain the three-phase voltage and current of the grid-connected point of the AC / DC converter in each substation, and obtain the three-phase voltage set and the three-phase current set.

[0165] The second module is used to obtain the active power shortage and reactive power shortage of each substation area according to the three-phase voltage set.

[0166] The third module is used to obtain a first data set based on the active power shortage of each substation combined with primary unbalanced power control and secondary load balancing operation control; the first data set includes active power reference input values ​​of each phase of the AC / DC converter of each substation.

[0167] The fourth module is used to obtain a second data set based on the reactive power shortage of each substation and the first data set; the second data set includes a three-phase current management reference value of each substation.

[0168] The fifth module is used to obtain a third data set according to the three-phase current set and the second data set; the third data set includes the zero-sequence voltage and output voltage of the AC / DC converter in each substation area. Positive and negative sequence components in the coordinate system.

[0169] The sixth module is used to obtain the switching signals of the four bridge arms of the AC / DC converter in each substation according to the third data set, and control the AC / DC converter in each substation according to the switching signals to achieve comprehensive management of three-phase imbalance and light and heavy loads.

[0170] The three-phase unbalanced and light-and-heavy load comprehensive optimization control device for a multi-station interconnected power distribution system of the present invention is used in the method of the present invention and has the same beneficial effects as the method of the present invention.

[0171] Verification part:

[0172] See also Figure 7 Taking the interconnection of two substations as an example, a simulation model is built in MATLAB / Simulink. The AC loads of substations 1 and 2 contain unbalanced loads, and the DC side includes DC loads such as photovoltaics, energy storage, and electric vehicles. The three-phase voltage on the secondary side of the substation transformer is 380V effective value, and the frequency is 50Hz. Assume that the transformer capacity of substation 1 is 80kVA, and the control mode is Control (constant DC bus voltage control), the transformer capacity of station area 2 is 40kVA, and the control mode is PQ Control (active and reactive power control).

[0173] In the preferred embodiment of the present invention, it is assumed that: when the load rate x of the AC / DC transformer in the substation is 25%≤x≤75%, the substation is in the optimal economic operation state; when the load rate x of the AC / DC transformer in the substation is x<25%, the substation is in light load operation; when the load rate x of the AC / DC transformer in the substation is x>75%, the substation is in heavy load operation.

[0174] In order to demonstrate the superiority of the present invention in the comprehensive optimization of three-phase imbalance and light and heavy loads when multiple substations are interconnected, it is assumed that the power on the DC side can just meet the DC load under the coordination of photovoltaics and energy storage. At this time, it can be equivalent to the real-time two-way power flow between low-voltage substations.

[0175] First, in order to demonstrate the effect of the present invention in three-phase imbalance control, the load of area 1 is set to 6kW+1kVar for phase A, 7kW+1kVar for phase B, and 8kW+2kVar for phase C at the initial moment; the load of area 2 is set to 5kW+2kVar for phase A, 6kW+2kVar for phase B, and 8kW+3kVar for phase C. When the optimization method proposed by the present invention is not used, area 1 and area 2 operate independently at this time, and the voltage waveform of the grid connection point of the AC / DC converter of area 1 and area 2, that is, the voltage waveform of the secondary side of the area transformer, is as follows: Figure 8 and Fig. 9As shown, after using the method proposed by the present invention, the voltage waveforms of the AC / DC converter grid connection points of the substation area 1 and the substation area 2 are as follows: Fig.10 and Fig.11 As shown, it can be seen that the three-phase imbalance problem has been effectively controlled.

[0176] To demonstrate the effect of the present invention on the comprehensive optimization of three-phase imbalance and light and heavy loads, at 2s, the load of area 1 remains unchanged, and the load of area 2 increases to 10kW+2kVar for phase A, 11kW+2kVar for phase B, and 13kW+3kVar for phase C. At this time, the load rate of area 2 exceeds 75%, that is, it is in a heavy load operation state. After stable operation, the grid-side output power of area 1 and area 2 is as follows: Fig.12 As shown in Figure 1, the output power of the transformer in area 2 is less than 30kW, that is, the load rate is less than 75%, and it is in light load operation, indicating that the light and heavy load optimization goal has been achieved. At this time, the voltage waveform of the AC / DC converter grid connection point in area 1 is as follows: Fig.13 As shown, the three-phase output power is Fig.14 As shown; the voltage waveform of the AC / DC converter grid connection point in station area 2 is as follows Fig.15 As shown, the three-phase output power is Fig.16 As shown. Since the DC side does not provide active power to the substation 1 and the substation 2, the three-phase output power of the AC / DC converter of the substation 1 is negative, and the three-phase output power of the AC / DC converter of the substation 1 is positive, that is, the power flows between the substation 1 and the substation 2. It can be concluded that under the method of the present invention, the three-phase imbalance and light and heavy load phenomena can be effectively improved.

[0177] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A three-phase unbalanced and light and heavy load comprehensive optimization control method for a multi-station interconnected power distribution system, the system comprising a constant DC bus voltage control station area and at least one constant active and reactive power control station area; characterized in that: The method comprises: The actual values ​​of the three-phase voltage and current of the grid connection point of the AC / DC converter in each substation are obtained to obtain a three-phase voltage set and a three-phase current set; the active power shortage and reactive power shortage of each substation are obtained according to the three-phase voltage set; The first data set is obtained according to the active power shortage of each substation in combination with the primary unbalanced power control and the secondary load-balancing operation control, including: obtaining the active power reference command value of each phase of the AC / DC converter in the substation for controlling the three-phase imbalance based on the primary unbalanced power control according to the active power shortage; the secondary load-balancing operation control is to obtain the active power reference input value of each phase of the AC / DC converter in the substation according to the active power reference command value and the operation state of the substation; the first data set includes the active power reference input value of each phase of the AC / DC converter in each substation; A second data set is obtained according to the reactive power shortage of each substation and the first data set; the second data set includes a three-phase current management reference value of each substation; A third data set is obtained based on the three-phase current set and the second data set; the third data set includes the zero-sequence voltage and output voltage of the AC / DC converter in each substation area. dq Positive and negative sequence components in the coordinate system; The switching signals of the four bridge arms of the AC / DC converter in each substation are obtained according to the third data set, and the AC / DC converter in each substation is controlled according to the switching signals to achieve comprehensive management of three-phase imbalance and light and heavy loads.

2. The three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-station interconnected power distribution system according to claim 1 is characterized in that: The active power shortage of each area includes: Obtaining the active power shortage of each substation according to the three-phase voltage set includes: Decompose the actual value of the three-phase voltage according to the symmetrical component method to obtain Positive sequence voltage in the coordinate system and ; The positive sequence voltage and From still The coordinate system is transformed back to the three-phase coordinate system to obtain the voltage reference value of each phase and ; The actual value of the three-phase voltage is expressed as and ;Will and and and and The phase angle deviations are expressed as and ; Will and After PI adjustment, the initial reference command value of active power of each phase can be obtained, that is, the active power shortage , ; By solving each substation, the active power shortage of each substation can be obtained.

3. The three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-station interconnected power distribution system according to claim 2 is characterized in that: The reactive power shortage of each area includes: Obtaining the reactive power shortage of each substation according to the three-phase voltage set includes: Calculate the effective value of each phase of the three-phase voltage actual value With each phase voltage reference value The voltage RMS deviation; The voltage effective value deviation is adjusted by PI to obtain the Phase reactive power reference command value, i.e. reactive power shortage , ; By solving each substation, the reactive power shortage of each substation can be obtained.

4. The three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-station interconnected power distribution system according to claim 3 is characterized in that: The first data set obtained according to the active power shortage of each substation combined with the primary unbalanced power control and the secondary load balancing operation control includes: A fourth data set is obtained based on the primary unbalanced power control according to the active power shortage of each substation; the fourth data set includes active power reference command values ​​of each phase for each substation AC / DC converter to control three-phase imbalance; The first data set is obtained based on the second load balancing operation control according to the fourth data set.

5. The three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-area interconnected power distribution system according to claim 4 is characterized in that: The fourth data set obtained based on the active power shortage of each substation area and the primary unbalanced power control includes: Get the real-time power flowing from the DC side to the AC side ; According to the active power shortage Based on the primary unbalanced power control, the active power reference command value of each phase of the AC / DC converter in the substation area is obtained to control the three-phase imbalance. , , which can be expressed as: ; ; ;in, express Phase active power shortage; express Phase active power shortage; express Phase active power shortage; solving each substation area, the fourth data set can be obtained.

6. The three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-station interconnected power distribution system according to claim 5 is characterized in that: The first data set is obtained based on the secondary load balancing operation control according to the fourth data set, including: The secondary load balancing operation control is based on the active power reference command value Get the active power reference input value of each phase of the AC / DC converter in the substation area Assuming the area The active power reference command value is , the active power reference input value is The actual load is , the transformer capacity is Assuming that there is a total Each area is interconnected, ; If the operation status of the substation includes the optimal economic operation status, light load operation status and heavy load operation status, then the active power reference input value is exist: Scenario 1: All stations are in the same operating state; It can be expressed as: ; Scenario 2: Each area is in the best economic operation state. The substation is in light load operation state, but at this time The load power required for each transformer in the substation to increase to 25% load rate is less than or equal to The load power required to be transferred when the load factor of each area drops to 25%; In the second scenario, if the In the best economic operation state, It can be expressed as: ; In the second scenario, if the In light load operation, It can be expressed as: ; Scenario 3: Each area is in the best economic operation state. The substation is in light load operation state, but at this time The load power required for the transformer in each area to increase to 25% load factor is greater than The load power required to be transferred when the load factor of each area drops to 25%; In case 3, if the Taiwan area In the best economic operation state, It can be expressed as: ; In case 3, if the Taiwan area In light load operation, It can be expressed as: ; Scenario 4: Each area is in the best economic operation state. The area is in heavy load operation, but at this time The load power required to be transferred when the load factor of each transformer in the substation is reduced to 75% is less than or equal to The load power required to increase the load factor of each area to 75%; In case 4, if the Taiwan area In the best economic operation state, It can be expressed as: ; In case 4, if the Taiwan area In heavy load operation, It can be expressed as: ; Scenario 5: Each area is in the best economic operation state. The area is in heavy load operation, but at this time The load power required to transfer from the transformer in each area to 75% load factor is greater than The load power required to increase the load factor of each area to 75%; In case 5, if the Taiwan area In the best economic operation state, It can be expressed as: ; In case 5, if the Taiwan area In heavy load operation, It can be expressed as: ; Scenario 6: Each area is in light load operation state. Each area is in heavy load operation; In case 6, if the Taiwan area In light load operation, It can be expressed as: ; In case 6, if the Taiwan area In heavy load operation, It can be expressed as: ; The first data set can be obtained by solving each station area.

7. The three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-station interconnected power distribution system according to claim 6 is characterized in that: The second data set obtained according to the reactive power shortage of each substation area and the first data set includes: The three-phase current management reference value in the second data set It can be expressed as: ; in, , Indicates The reactive power reference command value of each phase, i.e., the reactive power shortage; Indicates the AC / DC converter grid-connected i The effective value of the phase voltage; Indicates the phase of the positive sequence component of the grid fundamental frequency output by the phase-locked loop in real time; ; Indicates The angle between the phase voltage and current; The second data set can be obtained by solving each station area.

8. The three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-station interconnected power distribution system according to claim 7 is characterized in that: Obtaining a third data set according to the three-phase current set and the second data set includes: The three-phase current actual value of the three-phase current set and the three-phase current management reference value in the second data set are transformed into a stationary Coordinate system, the Clark transformation can be expressed as: ;get Positive sequence reference current in the coordinate system and , negative sequence reference current and , zero sequence reference current , Positive sequence actual current and and negative sequence actual current and ; and obtain the actual zero-sequence current ; Will The positive sequence reference current, negative sequence reference current, positive sequence actual current and negative sequence actual current in the coordinate system are from the static Coordinate transformation to rotation Coordinate system, the expression of transformation can be expressed as: ; in, Indicates the grid angular frequency; Indicates time; represents the rotation angle; Rotation angle when positive sequence reference current and positive sequence actual current are transformed The phase of the positive sequence component of the grid fundamental frequency output by the phase-locked loop in real time ,get and ; Rotation angle when negative sequence reference current and negative sequence actual current are transformed for ,get and ; Perform current inner loop control to obtain the output voltage of the AC / DC converter in the station area. Positive and negative sequence components in the coordinate system: If the AC / DC converter in the substation is controlled by a fixed DC bus voltage, the output voltage of the AC / DC converter is The positive sequence component in the coordinate system is and , the negative sequence component is and , which can be expressed as: ； ； ； ； If the AC / DC converter in the substation is controlled by fixed active and reactive power, the output voltage of the AC / DC converter is dq The positive sequence component in the coordinate system is and , the negative sequence component is and , which can be expressed as: ； ； ； ； in, and Indicates the PI parameters of the PI regulators of the first bridge arm, the second bridge arm and the third bridge arm of the AC / DC converter; represents a complex frequency domain variable; and Indicates the PI parameters of the DC bus voltage PI regulator; Indicates the DC bus voltage value; Indicates the DC bus voltage reference value; Indicates the inductance value of the LC filter in the AC / DC converter; The output voltage of the fourth bridge arm of the AC / DC converter, i.e., the zero-sequence voltage It can be expressed as: ;in, Indicates the parameters of the fourth bridge arm P regulator of the AC / DC converter; The third data set can be obtained by solving each station area.

9. The three-phase unbalanced and light- and heavy-load comprehensive optimization control method for a multi-area interconnected power distribution system according to claim 8 is characterized in that: The switching signals of the four bridge arms of the AC / DC converter in each area obtained according to the third data set include: According to the AC / DC converter output voltage The positive sequence component and the negative sequence component in the coordinate system are respectively subjected to inverse Park transformation and then added to obtain the three-phase voltage reference value in the abc coordinate system; The three-phase voltage reference value under the abc coordinate and the zero-sequence voltage are pulse-width modulated to obtain switching signals of the first three bridge arms and the fourth bridge arm of the AC / DC converter respectively.

10. A three-phase unbalanced and light-load and heavy-load comprehensive optimization control device for a multi-station interconnected power distribution system, used in the method according to any one of claims 1 to 9, characterized in that: The device comprises a first module, a second module, a third module, a fourth module, a fifth module and a sixth module; The first module is used to obtain the three-phase voltage and current of the grid connection point of the AC / DC converter in each substation area, and obtain a three-phase voltage set and a three-phase current set; The second module is used to obtain the active power shortage of each substation and the reactive power shortage of each substation according to the three-phase voltage set; The third module is used to obtain a first data set according to the active power shortage of each substation combined with primary unbalanced power control and secondary load balancing operation control; the first data set includes active power reference input values ​​of each phase of the AC / DC converter of each substation; The fourth module is used to obtain a second data set according to the reactive power shortage of each substation and the first data set; the second data set includes a three-phase current management reference value of each substation; The fifth module is used to obtain a third data set according to the three-phase current set and the second data set; the third data set includes the zero-sequence voltage and output voltage of each AC / DC converter in each substation. Positive and negative sequence components in the coordinate system; The sixth module is used to obtain the switching signals of the four bridge arms of the AC / DC converter in each substation according to the third data set, and control the AC / DC converter in each substation according to the switching signals to achieve comprehensive management of three-phase imbalance and light and heavy loads.

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