CN105071420A - Distribution transformer three-phase current dynamic balancing apparatus and work method thereof - Google Patents

Abstract

A three-phase current dynamic balancing device for a distribution transformer and a working method thereof. It relates to a medium and low voltage current balance device, in particular to a three-phase current dynamic balance device. Automatically realize the balance of the low-voltage power supply network, with strong scalability, high reliability, and high precision of dynamic compensation. Including module unit, current acquisition unit, remote communication unit and human-computer interaction unit. The modular units are connected in parallel to the public connection point of the power grid; the modular units include LCL filters, inverters, drive circuits and central controllers. The central controller, drive circuit, inverter and LCL filter are connected in sequence. Real-time monitoring, real-time and comprehensive reflection of load conditions, timely and accurate feedback of current conditions to the central controller, the central controller can adjust the three-phase load current in real time, dynamically and accurately, and improve the accuracy of dynamic current adjustment; flexibly increase or decrease the operation Modules reduce product power consumption and save energy.

Description

A distribution transformer three-phase current dynamic balance device and its working method

technical field

The invention relates to a middle and low voltage current balancing device and its working method, in particular to a three-phase current dynamic balancing device and its working method.

Background technique

There are a large number of single-phase loads in the low-voltage distribution network. Due to the unbalanced distribution of single-phase loads and the asynchronous input, the imbalance of three-phase loads has become a prominent problem in the operation and maintenance of low-voltage power grids. The unbalanced three-phase load will increase the loss of the power grid, seriously affect the quality of power supply, and cause harm to the low-voltage power grid, distribution transformers, and 10-35kV high-voltage lines. With the development of social economy and the improvement of people's living standards, a large number of high-power single-phase household appliances such as: air conditioners, water heaters, microwave ovens, induction cookers, etc. have entered ordinary families. These household appliances bring people comfort, convenience and fast life. At the same time, it caused a surge in single-phase load, which further exacerbated the impact of three-phase load imbalance in the low-voltage power supply system. The three-phase imbalance of the low-voltage power grid has always been the main problem that plagues the power supply unit.

The three-phase load balancing work of low-voltage distribution network has received more and more attention and attention from the power sector, but limited by the existing technical level and measuring instruments, the balancing work of low-voltage three-phase loads still only stays in the periodical test and Adjust the load based on experience, and the balance point only focuses on the balance at a few test points such as the transformer low-voltage side outlet, without considering the internal balance of the low-voltage power supply network, so the adjustment effect is not obvious.

Contents of the invention

Aiming at the above problems, the present invention provides a distribution transformer three-phase current dynamic balancing device and a working method thereof that automatically realizes balancing of a low-voltage power supply network, has strong scalability, high reliability, and high dynamic compensation precision.

Technical scheme of the present invention is:

It includes several modular units, current acquisition units, remote communication units and human-computer interaction units, and is characterized in that the modular units are connected in parallel to the common connection point of the power grid;

The module unit includes an LCL filter, an inverter, a drive circuit, a forced air-cooled radiator and a central controller;

The LCL filter is connected to the grid;

The central controller, drive circuit, inverter and LCL filter are connected in sequence;

The central controller is provided with a voltage detection device;

The voltage detection device is connected to the inverter;

A current detection device is connected between the current acquisition unit and the power grid,

The remote communication unit and the man-machine interaction unit are respectively connected with the central controller.

The LCL filter includes three capacitor branches, three resonant absorbing branches, a grid-side inductance and an outlet-side inductance;

The three capacitor branches are Y-shaped connections;

The three capacitor branches are respectively connected in parallel with the three resonance absorbing branches;

The network port side inductance and the outlet side inductance are respectively connected in series with the capacitor branch.

The capacitor branch includes a capacitor and a capacitor resistor;

The capacitor and the capacitor resistor are connected in series;

The connection node of the Y-type connection is located on the side of the capacitor and the resistor.

The resonance absorption branch includes an inductance and an inductance resistance;

The inductor resistance is connected in series with the inductor.

Described central controller comprises DSP module and FDGA module;

The DSP module and the FPGA module are connected to each other to realize mutual communication.

There is an RS485 communication interface on the DSP module;

The RS485 communication interface is connected with the remote communication unit to realize mutual communication.

The human-computer interaction unit is provided with an RS485 communication interface, and communicates with the DSP module through the remote communication unit.

The inverter includes a three-phase power unit and two DC side voltage support capacitors;

The two DC side voltage support capacitors are connected in series;

The three-phase power unit is connected in parallel with the two DC side voltage supporting capacitors.

The forced air cooling radiator is connected with the central controller.

Work as follows:

1) The current detection device detects the unbalanced component of the power grid on the load side;

2) The current detection device transmits the unbalanced component to the central controller through the current acquisition unit;

3) The central controller calculates the command current component;

4) The module unit generates a compensation component with the same amplitude and opposite direction according to the command current component;

5) The compensation component is filtered by the LCL filter and then input to the power grid;

6) The compensation component and the unbalanced component cancel each other out to eliminate the grid current on the load side.

In the present invention, the current detection device is used to monitor the three-phase load current of the low-voltage power supply line in real time at all times, which can fully reflect the load situation, and timely and accurately feed back the current situation to the central controller, so that the central controller can real-time, dynamic, Accurately adjust the three-phase load current, which greatly improves the accuracy of dynamic current adjustment; adopts modular design to form a redundant system, and can increase or decrease the operational modules according to the usage conditions, thereby improving the reliability of the device and reducing product performance. consumption, save energy, improve the scalability of the device, and have high promotion and application value and social and economic benefits.

Description of drawings

Fig. 1 is a structural representation of the present invention,

Figure 2 is a schematic diagram of the structure of the module unit,

Figure 3 is a schematic diagram of the structure of the LCL filter,

Figure 4 is a schematic diagram of the structure of the inverter,

Fig. 5 is a schematic diagram of the system composition of the present invention,

Figure 6 is a schematic diagram of the command current operation of the central controller,

Fig. 7 is a schematic diagram of triangular carrier comparison control,

Figure 8 is a schematic diagram of DC side voltage control,

Fig. 9 is a schematic diagram of voltage equalization control of the DC side voltage support capacitor;

In the figure, 1 is the module unit, 2 is the current acquisition unit, 3 is the remote communication unit, 4 is the human-computer interaction unit, 5 is the public connection point of the power grid, 101 is the central controller, 102 is the LCL filter; 103 is the inverter , 104 is a voltage detection device, 105 is a forced air-cooled radiator, 106 is a drive circuit, 1021 is a capacitor branch, 1022 is a resonance absorption branch, 1023 is an inductor on the network port side, 1024 is an inductor on the outlet side, and 1031 is a three-phase In the power unit, 1032 is a DC side voltage supporting capacitor, and 201 is a current detection device.

Detailed ways

As shown in Figures 1-4 of the present invention, the transformer is connected to the power grid, and the high-voltage electricity is delivered to the load after being stepped down by the transformer. The present invention is connected in parallel on the grid public connection point 5 between the transformer and the load. It includes several module units 1, current acquisition unit 2, remote communication unit 3, and human-computer interaction unit 4, and the module unit 1 is connected in parallel to the grid common connection point 5; the module unit 1 includes an LCL filter 102, an inverter 103 , driving circuit 106, forced air-cooled radiator 105 and central controller 101; the LCL filter 102 is connected with the grid; the inverter 103 is connected with the LCL filter 102 and the central controller 101 respectively; the central control The device 101 is connected to the forced air cooling radiator 105 and the drive circuit 106 respectively; the central controller 101 is connected to the current acquisition unit 2; the central controller 101 is provided with a voltage detection device 104; The unit 2 has a current detection device 201 connected thereto; the current detection device 201 is placed on the grid near the load side. The current detection device 201 is connected to the power grid; the remote communication unit 3 and the human-computer interaction unit 4 are respectively connected to the central controller 101 .

The load is a three-phase unbalanced load, which generates harmonics and reactive power at the same time, endangering the safety of the power grid. The three-phase current dynamic balance device is connected in parallel on the line, through the current acquisition unit 2 and the current detection device 201, the current detection algorithm based on the instantaneous reactive power theory is used to calculate the unbalanced component of the load current i _L , and use it as a three-phase The current command i _c * of the current balance device, let the current i _c = i _c * on the side of the three-phase current balance device, and then the three-phase balance of the current i _s on the grid side can be realized. The current acquisition unit 2 and the current detection device 201 can realize real-time monitoring, so the three-phase current dynamic balance device can realize real-time adjustment and improve the adjustment accuracy.

The LCL filter 102 includes three capacitor branches 1021, three resonance absorbing branches 1022, a grid-side inductance 1023 and an outlet-side inductance 1024; the three capacitor branches 1021 are Y-connected; the three capacitor The branch 1021 is connected in parallel with the three resonant absorbing branches 1022 respectively; the network port side inductance 1023 and the outlet side inductance 1024 are respectively connected in series with the capacitance branch 1021 .

The capacitor branch 1021 includes a capacitor and a capacitor resistor; the capacitor and the capacitor resistor are connected in series; the connection node of the Y-shaped connection is located on one side of the capacitor resistor.

The resonance absorbing branch 1022 includes an inductor and an inductor resistor; the inductor resistor is connected in series with the inductor.

The central controller includes a DSP module and an FDGA module; the DSP module and the FDGA module are connected to each other to realize mutual communication.

There is an RS485 communication interface on the DSP module; the RS485 communication interface is connected with a remote communication unit to realize mutual communication.

The human-computer interaction unit 4 is provided with an RS485 communication interface, and communicates with the DSP module through the remote communication unit.

The inverter 103 includes a three-phase power unit 1031 and two DC side voltage support capacitors 1032; the two DC side voltage support capacitors 1032 are connected in series; the three-phase power unit 1031 and the two DC side The voltage supporting capacitors 1032 are connected in parallel.

As shown in FIG. 2 , it is a schematic diagram of the internal structure connection of the module unit 1 . The module unit 1 includes an LCL filter 102, an inverter 103, a drive circuit 106, a forced air-cooled radiator 105, and a central controller 101; the LCL filter 102 is connected to the grid; the inverter 103 is connected to the LCL filter The device 102 is connected to the central controller 101 respectively; the central controller 101 is connected to the forced air cooling radiator 105 and the drive circuit 106 respectively; the central controller 101 is connected to the current acquisition unit 2; the central The controller 101 is provided with a voltage detection device 104; the central controller 101 sends instructions to the drive circuit 105, and the drive circuit drives the LCL filter 102, the inverter 103, and the forced air-cooled radiator 105 to work. The function of the LCL filter 102 is to filter the clutter in the power grid that can endanger the safe operation of the power grid. The function of the inverter 103 is to invert the filtered direct current into an alternating current with the same amplitude and phase as the alternating current in the power grid and then feed back to the grid. The forced air cooling radiator 105 can quickly cool down the module unit 1 when the module unit 1 is overheated, so as to ensure the normal operation of the module unit 1 .

The LCL filter 102 and the inverter 103 together constitute a main circuit. A three-phase bridge circuit composed of fully-controlled power electronic devices IGBT is used to control the on and off of the IGBT through PWM pulses, so that the device can output a specific current.

As shown in Figure 3, it is a schematic diagram of the structure of the LCL filter. Including three capacitance branches 1021, three resonant absorption branches 1022, grid side inductance 1023 and outlet side inductance 1024; the three capacitance branches 1021 are Y-shaped connections; the three capacitance branches 1021 are connected with the three The resonant absorbing branches 1022 are respectively connected in parallel; the network port side inductance 1023 and the outlet side inductance 1024 are respectively connected in series with the capacitor branch 1021 .

The capacitor branch 1021 includes a capacitor and a capacitor resistor; the capacitor and the capacitor resistor are connected in series; the connection node of the Y-shaped connection is located on one side of the capacitor resistor.

The resonance absorbing branch 1022 includes an inductor and an inductor resistor; the inductor resistor is connected in series with the inductor.

As shown in Figure 4, it is a schematic diagram of the structure of the inverter. Including a three-phase power unit 1031 and two DC-side voltage support capacitors 1032; the two DC-side voltage support capacitors 1032 are connected in series; the three-phase power unit 1031 is connected in parallel with the two DC-side voltage support capacitors 1032 . The outlet of the inverter should be connected to the grid-side inductance of the LCL filter.

As shown in Figure 5, e _s represents the voltage at the low-voltage outlet side of the distribution transformer. The load is a three-phase unbalanced load, which generates harmonics and consumes reactive power at the same time. The three-phase current balance device is connected in parallel on the line. Through the current detection algorithm based on the instantaneous reactive power theory, the unbalanced component in the load current i _L is calculated, and it is used as the current command _ic * of the three-phase current balance device, and through the current detection algorithm based on the instantaneous reactive power theory The three-phase current i _s balance of the grid side can be achieved by making the current _{ic on the device side of the three-phase current balance = i c *} .

The control circuit is the central controller, including the instruction current operation circuit and the current tracking control circuit. The core of the instruction current operation circuit is to calculate the unbalanced component, reactive component and harmonic component in the load current i _L , and use it as the current instruction i _c * of the device; the core of the current tracking control circuit is the current controller, the control device The output current _ic quickly and accurately tracks its command current _ic *, and its output is a series of PWM signals.

The function of the drive circuit is to amplify the PWM signal generated by the current tracking control circuit and isolate the control circuit (weak current part) from the main circuit (strong current part). The PWM pulse output by the drive circuit can drive the IGBT in the main circuit , Generate corresponding compensation current _ic and send it to the power grid to eliminate imbalance.

The dq coordinate transformation matrix and its inverse transformation matrix are shown in the following formulas:

The extracted fundamental current component is:

In this way, the extracted compensation current command is:

As shown in Figure 6, the calculation of the command current is based on the theory of instantaneous reactive power, and the load current is sampled, and the final compensation current command is obtained through a certain coordinate change.

Pass the grid voltage of phase A through the phase-locked loop (PLL) to obtain the relevant information of the time variable (ωt), that is, the position of the rotating voltage vector in the three-phase abc coordinate system. Transform the detected three-phase load currents iLa, iLb, iLc from the three-phase abc coordinate system to the two-phase dq coordinate system that rotates synchronously with the fundamental angular frequency (ω) of the phase voltage of the power grid. The d-axis is oriented to the direction of the voltage vector. Therefore, the current component id transformed to the d-axis is the active current component, the component iq transformed to the q-axis is the reactive current component, and i0 is the zero-sequence current component. After coordinate transformation, the nth positive sequence component of the three-phase abc coordinate system will become the (n-1)th component in the two-phase dq synchronous rotating coordinate system; and the nth negative sequence component of the three-phase abc coordinate system After the coordinate transformation, the component will become the (n+1)th component in the two-phase dq synchronous rotating coordinate system. In this way, among all the components, only the positive sequence component of the fundamental wave becomes DC in the synchronous coordinate system, while the other components are still AC; the DC can be extracted by a low-pass filter (LPF). For the DC component of the d-axis component , representing the fundamental active current component, the (d-axis command), 0 (q-axis command), 0 (zero-axis command) transform from the two-phase dq coordinate system to the three-phase abc coordinate system to obtain the three-phase fundamental wave active current iaf, ibf, icf, that is, the grid side only wants current component. According to the circuit KCL law, subtract the load current from the desired grid side current to obtain the compensation current that the device needs to send out.

As shown in Figure 7, the current tracking control of the central controller adopts triangular carrier control. Its control principle is to compare the actual compensation current ic of the ^device with the command current ic _* , send its deviation _Δi to the current loop controller to obtain the modulated wave signal, compare the modulated signal with the triangular carrier wave in real time, and generate PWM Signal. After the PWM signal is amplified by the drive circuit, it can drive the IGBT in the three-phase bridge circuit, and the three-phase bridge circuit outputs the corresponding voltage waveform, and the difference between the voltage and the grid voltage acts on the output reactor, then Generate the required compensation current waveform.

As shown in Figure 8, it is a control schematic diagram of the DC side voltage. Since the device must absorb active energy from the system to maintain the stability of the capacitor voltage, the compensation current sent by the device must contain active current components. Compare the DC side voltage command value Udc* with the DC side voltage value Udc, and send the deviation △Udc to the voltage controller for adjustment. The output △id of the voltage controller is the active component of voltage regulation, which is added to the voltage shown in Figure 1 of In this method, the compensation current command of the device contains the active current component required for voltage stabilization, so as to maintain the constant voltage of the DC side of the three-phase bridge circuit.

As shown in FIG. 9 , the voltage of the DC side voltage supporting capacitor 1032 is adjusted by adjusting the zero line current of the device. Among them, U _{dc 1} and U _{dc 2} represent the voltage values of the upper and lower capacitors on the DC side of the device respectively, and the difference is sent to the voltage controller to obtain Δ i ₀ , which is divided into three parts and superimposed on Fig. 5, so that a DC component appears in the zero line current command of the device, so as to maintain the voltage balance of the voltage of the DC side voltage supporting capacitor 1032 .

The three-phase current dynamic balance device of the distribution transformer uses a current detection device to monitor the three-phase load current of the low-voltage power supply line in real time at all times, which can fully reflect the load situation, and timely and accurately feed back the current situation to the central controller, so that the central control The controller can adjust the three-phase load current in real time, dynamically and accurately, which greatly improves the accuracy of dynamic current adjustment; it adopts a modular design to form a redundant system, and can increase or decrease the operational modules according to the usage conditions, thereby improving the reliability of the device It reduces the power consumption of the product, saves energy, improves the scalability of the device, and has high promotion and application value and social and economic benefits.

Claims (10)

1. A distribution transformer three-phase current dynamic balancing device comprises a plurality of module units, a current acquisition unit, a remote communication unit and a human-computer interaction unit, and is characterized in that the module units are connected in parallel to a public connection point of a power grid;

the module unit comprises an LCL filter, an inverter, a driving circuit, a forced air cooling radiator and a central controller;

the LCL filter is connected with a power grid;

the central controller, the driving circuit, the inverter and the LCL filter are sequentially connected;

the central controller is provided with a voltage detection device;

the voltage detection device is connected with the inverter;

a current detection device is connected between the current acquisition unit and the power grid,

the remote communication unit and the man-machine interaction unit are respectively connected with the central controller.

2. The distribution transformer three-phase current dynamic balancing apparatus of claim 1, wherein the LCL filter comprises three capacitive branches, three resonant absorption branches, a grid-side inductor and an outlet-side inductor;

the three capacitor branches are connected in a Y shape;

the three capacitor branches are respectively connected with the three resonance absorption branches in parallel;

and the network port side inductor and the outlet side inductor are respectively connected with the capacitor branch circuits in series.

3. The distribution transformer three-phase current dynamic balancing apparatus of claim 2, wherein the capacitive branch comprises a capacitor and a capacitor resistor;

the capacitor and the capacitor resistor are connected in series;

and the connection node of the Y-shaped connection is positioned on one side of the capacitor resistor.

4. The distribution transformer three-phase current dynamic balancing apparatus of claim 2, wherein the resonance absorption branch comprises an inductor and an inductor resistor;

the inductor resistor is connected in series with the inductor.

5. The distribution transformer three-phase current dynamic balancing apparatus of claim 1, wherein the central controller comprises a DSP module and an FDGA module;

and the DSP module and the FDGA module are mutually connected to realize mutual communication.

6. The distribution transformer three-phase current dynamic balancing device of claim 3, wherein the DSP module is provided with an RS485 communication interface;

and the RS485 communication interface is connected with the remote communication unit to realize mutual communication.

7. The distribution transformer three-phase current dynamic balancing device of claim 3, wherein the human-computer interaction unit is provided with an RS485 communication interface, and the communication with the DSP module is realized through a remote communication unit.

8. The distribution transformer three-phase current dynamic balancing apparatus of claim 3, wherein the inverter comprises a three-phase power unit and two DC side voltage support capacitors;

the two direct-current side voltage supporting capacitors are connected in series;

the three-phase power unit is connected with the two direct-current side voltage supporting capacitors in parallel.

9. The distribution transformer three-phase current dynamic balancing apparatus of claim 3, wherein the forced air cooling radiator is connected to the central controller.

10. The operation method of the distribution transformer three-phase current dynamic balancing device according to claim 3, characterized by comprising the following steps:

1) the current detection device detects the unbalanced component of the load side power grid;

2) the current detection device transmits the unbalanced component to the central controller through the current acquisition unit;

3) the central controller calculates a command current component;

4) the module unit generates compensation components with the same amplitude and opposite directions according to the command current component;

5) the compensation component is filtered by an LCL filter and then is input into a power grid;

6) the compensation component and the unbalance component are mutually offset, and the load side power grid current is eliminated.