Power distribution network voltage sag fast compensation method and system based on hybrid distribution transformer

Abstract

The application relates to a power distribution network voltage sag fast compensation method based on a hybrid distribution transformer, which comprises the following steps: collecting and detecting three-phase voltage and phase on the power distribution network side; judging whether a voltage compensation system needs to be driven, determining the value of the required compensation voltage if the voltage compensation system needs to be driven; starting the voltage compensation system, taking the value of the required compensation voltage of the voltage compensation system as the output value of an inverter unit, using an SOGI phase-locked loop to control the size and phase of the voltage output by the inverter unit, and achieving the purpose of controlling the compensation system; and measuring the voltage and phase on the secondary winding side and verifying the compensation effect. The application further discloses a power distribution network voltage sag fast compensation system based on a hybrid distribution transformer. The application can accurately and timely collect the phase condition on the power distribution network side, can ensure timely detection of voltage sag conditions, has very good isolation effect, and the electric energy input from the auxiliary winding end of the hybrid distribution transformer comes from a photovoltaic unit and belongs to clean renewable energy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power quality analysis and recovery, and in particular to a power distribution network voltage sag fast compensation method and system based on a hybrid distribution transformer. BACKGROUND

[0002] With the increase of nonlinear loads in the power system and the problems of the low-voltage distribution network system itself, such as faults, voltage fluctuations and current harmonics often occur on the distribution network. According to relevant statistical surveys, 98% of all power quality problems and complaints are caused by voltage sags, voltage interruptions lasting 15 seconds or less. The problems caused by voltage sags, such as contactor tripping in substations, large factory areas, offices, and other areas, inverter shutdown, and inverter conversion failure, may cause huge economic losses and negative social impacts.

[0003] At present, the research scheme of the power grid voltage sag mainly includes the following: taking any one of the three-phase voltage of the distribution network and delaying several cycles to construct its orthogonal signal, cooperating with the ordinary phase-locked loop for dq transformation to quickly detect the depth of voltage sag. However, this method has a serious delay phenomenon because it uses delay to construct the orthogonal signal, and cannot accurately and timely detect the voltage sag. The double-loop vector decoupling control strategy can improve the dynamic performance of the voltage restorer in compensation. This method has better control effect and faster response speed, but the phase-locked loop for the distribution network voltage is not accurate and timely, resulting in errors in the compensation voltage. The incremental parameter fuzzy adaptive PID control based on fuzzy control design realizes adaptive PID control parameters to achieve good control effect and realize stable compensation voltage of the voltage recovery system. However, this method still has the problems of slow response speed and slow voltage recovery. SUMMARY

[0004] The primary purpose of the present application is to provide a power distribution network voltage sag fast compensation method based on a hybrid distribution transformer with faster response speed and better compensation effect.

[0005] To achieve the above purpose, the present application adopts the following technical solution: a power distribution network voltage sag fast compensation method based on a hybrid distribution transformer, which comprises the following sequential steps:

[0006] (1) Collect and detect the three-phase voltage and phase of the distribution network side, and convert the three-phase voltage into the distribution network side DC voltage quantity Ud and Uq through abc-dq transformation;

[0007] (2) According to the distribution network side DC voltage Ud and Uq, the distribution network side voltage effective value and phase are obtained by calculation, the distribution network side voltage effective value and phase are compared with the distribution network side rated voltage effective value and phase, whether the drive voltage compensation system is needed is judged, if the drive voltage compensation system is needed, the value of the compensation voltage required is determined;

[0008] (3) The voltage compensation system is started, the value of the compensation voltage required by the voltage compensation system is used as the output value of the inverter unit, the SOGI phase-locked loop is used in the control circuit to control the size and phase of the voltage output by the inverter unit, and the purpose of controlling the compensation system is achieved;

[0009] (4) The secondary winding side voltage and phase are measured to verify the compensation effect.

[0010] The step (1) specifically comprises the following steps:

[0011] (1a) Collecting any one phase voltage Uc of the three-phase voltage of the distribution network side, obtaining the other two-phase voltages Ua and Ub with the same amplitude and 120° phase difference by derivation of the phase voltage, and constructing three-phase voltage Ua, Ub, Uc;

[0012] (1b) The three-phase voltage Ua, Ub, Uc is subjected to abc-dq transformation to obtain the distribution network side DC voltage Ud and Uq.

[0013] The step (2) specifically comprises the following steps:

[0014] (2a) The distribution network side voltage effective value and phase are calculated:

[0015]

[0016]

[0017] The distribution network side voltage effective value U1 and phase are obtained The effective value U1 and phase are compared with the effective value and phase of the distribution network side rated voltage, if the calculated effective value U1 is more than 10% lower than the distribution network side rated voltage effective value, it is judged that the distribution network voltage sag fault occurs;

[0018] (2b) After the distribution network voltage sag fault occurs, the difference between the secondary winding side voltage value at this time and the rated secondary winding side voltage value, that is, the value of the compensation voltage required by the voltage compensation system, is determined.

[0019] The step (3) specifically refers to: the value of the compensation voltage required by the voltage compensation system determined in step (2) is used as the output value of the inverter unit, the SOGI phase-locked loop is used in the control circuit to control the voltage and phase required by the inverter unit, which is input into the auxiliary winding side of the hybrid distribution transformer, and the compensation purpose is achieved.

[0020] The step (4) is specifically to measure the voltage and phase of the secondary winding side in the simulation after compensation, compare the voltage with the voltage when the voltage sag fault of the power distribution network does not occur using a scope oscilloscope, and observe the compensation effect.

[0021] Another object of the present application is to provide a voltage compensation system based on a power distribution network voltage sag fast compensation method of a hybrid distribution transformer, comprising:

[0022] The hybrid distribution transformer is used for voltage transformation and coupling compensation system, and separates the power distribution network, the load and the compensation system;

[0023] The inverter unit is used for inverting the direct current voltage into alternating current voltage, and inputs the value and phase of the required compensation voltage to the auxiliary winding side of the hybrid distribution transformer;

[0024] The DC / DC conversion unit is used for boosting the direct current voltage stored by the photovoltaic unit, and provides the direct current bus voltage to the inverter unit;

[0025] The photovoltaic unit is used for collecting and storing electric energy, and providing energy;

[0026] The control circuit is used for detecting whether the voltage sag fault occurs, and is used for controlling the inverter unit and inputting the control signal to the inverter unit;

[0027] The hybrid distribution transformer comprises:

[0028] The primary winding is used for being directly connected with the star-shaped connection of the power distribution network;

[0029] The secondary winding is used for being directly connected with the delta-shaped connection of the load side;

[0030] The auxiliary winding is used for being connected with the output side of the inverter unit;

[0031] The output end of the photovoltaic unit is connected with the input end of the DC-DC conversion unit, the output end of the DC-DC conversion unit is connected with the input end of the inverter unit, and the input end of the control circuit is connected with the voltage of the power distribution network, and the output end of the control circuit is connected with the control end of the inverter unit.

[0032] From the above technical solution, the beneficial effects of the present application are: first, the single item derivation is used to construct three items, and the abc-dq transformation is carried out in cooperation with the SOGI phase-locked loop, the detection method is very short, there is no delay phenomenon, and the phase condition of the power distribution network side can be accurately and timely collected, and the voltage sag condition can be detected in time; second, the compensation voltage coupling mode of the present application is based on the hybrid distribution transformer, and has very good isolation effect, the energy input from the auxiliary winding end of the hybrid distribution transformer comes from the photovoltaic unit, which belongs to clean renewable energy. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a flow chart of the method of the present application;

[0034] Figure 2 is a schematic diagram of the system structure of the present application;

[0035] Figure 3 is a simulation diagram of the voltage sag on the power distribution network side;

[0036] Figure 4 is a simulation diagram of the compensation voltage of the compensation system;

[0037] Figure 5 is a simulation diagram of the voltage on the load side after compensation. DETAILED DESCRIPTION

[0038] As shown in Figure 1 , a power distribution network voltage sag fast compensation method based on a hybrid power distribution transformer, the method comprising the following sequential steps:

[0039] (1) Collect and detect the three-phase voltage and phase on the power distribution network side, and convert the three-phase voltage into the DC voltage quantity Ud and Uq on the power distribution network side through abc-dq transformation;

[0040] (2) According to the DC voltage quantity Ud and Uq on the power distribution network side, obtain the effective value and phase of the voltage on the power distribution network side through calculation, compare the effective value and phase of the voltage on the power distribution network side with the effective value and phase of the rated voltage on the power distribution network side, and determine whether the voltage compensation system needs to be driven, and if the voltage compensation system needs to be driven, determine the value of the compensation voltage required;

[0041] (3) Start the voltage compensation system, and use the value of the compensation voltage required by the voltage compensation system as the output value of the inverter unit 5, use SOGI phase-locked loop in the control circuit 8 to control the size and phase of the voltage output by the inverter unit 5, so as to achieve the purpose of controlling the compensation system;

[0042] (4) Measure the voltage and phase on the secondary winding 3 side to verify the compensation effect.

[0043] The step (1) specifically comprises the following steps:

[0044] (1a) Collect any one phase voltage Uc of the three-phase voltage on the power distribution network side, and obtain the other two phase voltages Ua and Ub with the same amplitude and 120° phase difference through derivation of this phase voltage, to construct the three-phase voltage Ua, Ub, Uc;

[0045] (1b) Perform abc-dq transformation on the three-phase voltage Ua, Ub, Uc to obtain the DC voltage quantity Ud and Uq on the power distribution network side.

[0046] The step (2) specifically comprises the following steps:

[0047] (2a) calculating the effective value and phase of the distribution network side voltage:

[0048]

[0049]

[0050] The effective value U1 and the phase of the distribution network side voltage are obtained Compared with the effective value and phase of the rated voltage of the distribution network side, if the calculated effective value U1 is more than 10% lower than the effective value of the rated voltage of the distribution network side, it is judged that the distribution network voltage sag fault occurs;

[0051] (2b) After determining that the distribution network voltage sag fault occurs, the difference between the voltage value of the secondary winding 3 side at this time and the rated voltage value of the secondary winding 3 side, that is, the value of the compensation voltage required by the voltage compensation system, is determined.

[0052] The step (3) specifically refers to: taking the value of the compensation voltage required by the voltage compensation system determined in the step (2) as the output value of the inverter unit 5, using the SOGI phase-locked loop in the control circuit 8 to control the voltage and phase required by the inverter unit 5 to output, and inputting the voltage and phase into the auxiliary winding 1 side of the hybrid distribution transformer to achieve the compensation purpose.

[0053] The step (4) specifically refers to: after the compensation is completed, the voltage and phase of the secondary winding 3 side are measured in simulation, and the scope oscilloscope is used to compare with the voltage when the distribution network voltage sag fault does not occur, and the compensation effect is observed.

[0054] Another object of the application is to provide a voltage compensation system based on a distribution network voltage sag fast compensation method of a hybrid distribution transformer, comprising:

[0055] The hybrid distribution transformer is used for voltage transformation and coupling compensation system, and separates the distribution network, the load 4 and the compensation system;

[0056] The inverter unit 5 is used for inverting the direct current voltage into alternating current voltage, and inputting the value and phase of the required compensation voltage into the auxiliary winding 1 side of the hybrid distribution transformer;

[0057] The DC / DC converter unit is used for boosting the direct current voltage stored by the photovoltaic unit 7, and providing the direct current bus voltage for the inverter unit 5;

[0058] The photovoltaic unit 7 is used for collecting and storing electric energy, and providing energy;

[0059] The control circuit 8 is used for detecting whether the sag fault occurs, and is used for controlling the inverter unit 5 and inputting the control signal into the inverter unit 5;

[0060] The hybrid distribution transformer includes:

[0061] Primary winding 2 is used for direct star connection to the power distribution network;

[0062] Secondary winding 3 is used for direct delta connection to the load 4 side;

[0063] Auxiliary winding 1 is used to connect to the output side of inverter unit 5;

[0064] The output terminal of the photovoltaic unit 7 is connected to the input terminal of the DC-DC converter unit 6, the output terminal of the DC-DC converter unit 6 is connected to the input terminal of the inverter unit 5, the input terminal of the control circuit 8 is connected to the distribution network voltage, and the output terminal of the control circuit 8 is connected to the control terminal of the inverter unit 5.

[0065] The following combination Figures 1 to 5 The present invention will be further described below.

[0066] The voltage value to be compensated is calculated to obtain the output value of inverter unit 5. Control circuit 8, in conjunction with SOGI phase-locked loop, outputs a suitable AC voltage into auxiliary winding 1 under the combined action of the phase of the grid voltage output by SOGI and the control signal output by control circuit 8. Simultaneously, auxiliary winding 1 generates magnetic flux within the hybrid transformer. By controlling the magnitude and phase of the AC voltage output by inverter unit 5, the magnitude of the magnetic flux generated by auxiliary winding 1 is controlled, thereby achieving the effect of controlling the coupling voltage and phase of the secondary circuit. The AC voltage is directly input to auxiliary winding 1, and voltage compensation is performed on secondary winding 3 through magnetic coupling. This compensation method not only provides isolation but also ensures that the output compensation voltage is in phase with the grid voltage after a voltage dip, and the amplitude reaches the grid's rated voltage value.

[0067] like Figure 1 As shown in control circuit 8, the SOGI phase-locked loop obtains the same phase as the primary distribution network. Based on this phase, a sin function with the same phase is constructed. The three-phase voltage constructed by differentiation is transformed by abc-dq to obtain the sag Ud. It is compared with the rated Ud corresponding to the rated voltage of the distribution network after abc-dq transformation. The difference is input to the PI regulator. The output value of the PI regulator is multiplied by the sinusoidal function with the same phase of the distribution network to obtain the modulation signal. The modulation signal is compared with the triangular wave to obtain the control signal. The inverter unit 5 needs to output a suitable AC voltage according to the phase of the distribution network output by the phase-locked loop and the control signal output by control circuit 8.

[0068] Combination Figure 2 and Figure 3Viewing the secondary winding 3 side voltage and phase, verifying the compensation effect, specifically refers to: first, build a distribution network simulation model of the hybrid distribution transformer, simulate the voltage sag of the distribution network, measure the voltage and phase of the secondary winding 3 side after compensation in the simulation, compare the voltage with the voltage when the distribution network voltage sag fault does not occur using the scope oscilloscope, and observe the compensation effect of this method. Figure 4 It can be seen that the simulation verifies that this method can accurately and quickly achieve the distribution network voltage sag compensation effect of the hybrid distribution transformer.

[0069] In summary, the present application adopts single item derivation to construct three items, and cooperates with SOGI phase-locked loop to carry out abc-dq transformation, the detection method is very short, there is no delay phenomenon, and the phase condition of the distribution network side can be accurately and timely collected, so that the voltage sag condition can be detected in time; The compensation voltage coupling method of the present application is based on the hybrid distribution transformer, has very good isolation effect, the electric energy input from the auxiliary winding 1 end of the hybrid distribution transformer comes from the photovoltaic unit 7, which belongs to clean renewable energy.

Claims

1. A method for rapid compensation of voltage sag in distribution networks based on hybrid distribution transformers, characterized in that: The method includes the following steps in sequence: (1) Collect and detect the three-phase voltage and phase on the distribution network side, and convert the three-phase voltage into DC voltage quantities Ud and Uq on the distribution network side through abc-dq transformation; (2) Based on the DC voltage Ud and Uq on the distribution network side, the effective value and phase of the voltage on the distribution network side are calculated. The effective value and phase of the voltage on the distribution network side are compared with the effective value and phase of the rated voltage on the distribution network side to determine whether a voltage compensation system needs to be driven. If a voltage compensation system needs to be driven, the value of the required compensation voltage is determined. (3) Start the voltage compensation system. The value of the compensation voltage required by the voltage compensation system is the output value of the inverter unit. In the control circuit, the SOGI phase-locked loop is used to control the magnitude and phase of the voltage output by the inverter unit to achieve the purpose of controlling the compensation system. (4) Measure the voltage and phase on the secondary winding side to verify the compensation effect; Step (1) specifically includes the following steps: (1a) Collect any one phase voltage Uc of the three-phase voltage on the distribution network side, and obtain the other two phase voltages Ua and Ub with the same amplitude and a phase difference of 120° by differentiating this phase voltage, and construct the three-phase voltages Ua, Ub and Uc; (1b) Perform abc-dq transformation on the three-phase voltages Ua, Ub, and Uc to obtain the DC voltages Ud and Uq on the distribution network side; Step (2) specifically includes the following steps: (2a) The effective value and phase of the voltage on the distribution network side are calculated: ； ； Obtain the effective value of the voltage on the distribution network side and phase Compare the effective value and phase with the rated voltage on the distribution network side. If the calculated effective value... If the voltage drops by more than 10% below the effective value of the rated voltage on the distribution network side, it is determined that a voltage sag fault has occurred in the distribution network. (2b) After a voltage dip fault occurs in the distribution network, measure the difference between the voltage value on the secondary winding side and the rated voltage value on the secondary winding side at this time, which is the value of the compensation voltage required by the voltage compensation system. The specific meaning of step (3) is: take the value of the compensation voltage required by the voltage compensation system determined in step (2) as the output value of the inverter unit, use SOGI phase-locked loop in the control circuit to control the output voltage and phase of the inverter unit, and input it to the auxiliary winding side of the hybrid distribution transformer to achieve the compensation purpose; The specific step (4) refers to: after the compensation is completed, measuring the voltage and phase on the secondary winding side in the simulation, comparing the voltage with that when the distribution network voltage sag fault does not occur using a scope oscilloscope, and observing the compensation effect.

2. A voltage compensation system implementing the fast voltage sag compensation method for distribution networks based on hybrid distribution transformers as described in claim 1, characterized in that: include: Hybrid distribution transformers are used in transformer and coupling compensation systems to isolate the distribution network, load, and compensation system. The inverter unit is used to convert DC voltage into AC voltage and input the required compensation voltage value and phase to the auxiliary winding side of the hybrid distribution transformer; The DC / DC converter unit is used to boost the DC voltage stored in the photovoltaic unit and provide the DC bus voltage to the inverter unit. Photovoltaic units are used to collect and store electrical energy to provide power. The control circuit is used to detect whether a transient fault has occurred and to control the inverter unit by inputting control signals to the inverter unit. The hybrid distribution transformer includes: The primary winding is used for direct star connection to the distribution network; The secondary winding is used for direct delta connection to the load side; Auxiliary winding, used to connect to the output side of the inverter unit; The output terminal of the photovoltaic unit is connected to the input terminal of the DC-DC converter unit, the output terminal of the DC-DC converter unit is connected to the input terminal of the inverter unit, the input terminal of the control circuit is connected to the distribution network voltage, and the output terminal of the control circuit is connected to the control terminal of the inverter unit. The output value of the inverter unit is calculated from the voltage value to be compensated. The control circuit, in conjunction with the SOGI phase-locked loop, outputs a suitable AC voltage into the auxiliary winding under the combined action of the phase of the grid voltage output by the SOGI phase-locked loop and the control signal output by the control circuit. At the same time, the auxiliary winding generates magnetic flux in the hybrid transformer. By controlling the magnitude and phase of the AC voltage output by the inverter unit, the magnitude of the magnetic flux generated by the auxiliary winding is controlled, thereby achieving the effect of controlling the coupling voltage and phase of the secondary circuit. The AC voltage is directly input into the auxiliary winding, and the voltage of the secondary winding is compensated through magnetic coupling. This compensation method not only provides isolation but also ensures that the output compensation voltage is in phase with the grid voltage after a voltage dip, and the amplitude reaches the grid's rated voltage value.

Images