CN107086786A - Interactive voltage stabilizing system and operation method for bidirectional energy flow - Google Patents

Abstract

The present invention provides a kind of voltage-stabilizing system for adjusting voltage ripple of power network, the system includes key load blocks, nonessential load blocks, two-way mutual electric power spring, multiple voltage detection modules, multiple current detection modules, a multiple phase detecting modules, the two-way mutual electric power spring and key load blocks and non-critical loads block coupled in series, power network is connected to by transfer wire.A kind of operating method for the voltage-stabilizing system for adjusting voltage ripple of power network is provided simultaneously.Beneficial effect is that the system does not need the participation of energy storage device but by bi-directional energy flow by the energy compensating of non-critical loads side to key load, to maintain the stabilization of key load both end voltage.Due to can compensate for the voltage of any phase angle, the frequency and phase of same rectifiable key both end voltage.Due to directly providing voltage compensation to key load, therefore the impedance partial pressure to transmission line requires low, and adjustable range is big, and cost is low, provides rational voltage and energy management for following distributed generation system, is conducive to the large-scale application of generation of electricity by new energy.

Description

Interactive voltage stabilizing system and operation method for bidirectional energy flow

technical field

The invention relates to the field of operation control of an AC power grid, in particular to an interactive voltage stabilizing system and an operation method for bidirectional energy flow, and a high-permeability new energy power supply grid.

Background technique

With the development of renewable energy (such as wind energy, solar energy, etc.) power generation technology, its grid-connected capacity is increasing year by year. For large-scale power grids, because of their strong self-regulation capabilities, and the proportion of renewable energy power generation is not large, the stability of the grid will not be greatly affected. For isolated microgrids with small capacity, the proportion of renewable energy power generation is often greater than 15%. If its irregularly changing output power cannot be balanced with the grid load, it will cause obvious fluctuations in the effective value of the grid voltage. The fluctuation of the effective value of the AC voltage will have adverse effects or even serious consequences on the stability of the power grid and the electrical equipment connected to the microgrid.

Traditional grid voltage regulation is based on energy storage devices to compensate for electrical energy. However, energy storage devices will significantly increase the cost, and due to the complex centralized compensation strategy, it is often difficult to achieve timely compensation.

In 2015, the electric spring appeared as a new concept. The electric spring is connected in series with the non-critical load, and the voltage stability of the critical load is achieved by compensating energy. The current electric springs are divided into two types: pure reactive power compensation and active and reactive power compensation.

Active and reactive power compensation also requires the support of energy storage devices. Due to frequent charging and discharging, the life of the energy storage devices will be reduced and the cost will be increased.

The electric spring for reactive power compensation does not need an energy storage device, but compensates for pure reactive power. This electric spring has a small adjustment range and has a large dependence on the impedance of the transmission line. The current on the large transmission line divides the line impedance too much to achieve voltage regulation, which will cause redundant losses.

Contents of the invention

In order to solve the above problems, the object of the present invention is to provide an interactive voltage stabilization system and operation method for bidirectional energy flow, which is a solution for active power and reactive power compensation, which can not only achieve the stability of critical voltage and frequency, but also It does not require energy storage devices such as batteries and has low dependence on line impedance, which can improve the utilization rate of new energy power generation and reduce costs.

In order to achieve the above purpose, the technical solution adopted by the present invention is to provide an interactive voltage stabilizing system with bidirectional energy flow, which includes a critical load module, a non-critical load module, a bidirectional interactive electric spring, multiple A voltage detection module, a plurality of current detection modules, and a phase detection module, the two-way interactive electric spring is connected in series with the critical load module and the non-critical load module, and connected to the power grid through a transmission wire; the two-way interactive electric spring is connected to the key The critical load module and the non-critical load module are connected in series with the power grid through the transmission wire; the voltage detection module is connected with the critical load module, the non-critical load module, the grid voltage, and two low-pass LC filters of the two-way interactive electric spring The capacitance of the device and the large capacitance of the two-way interactive electric spring are connected in parallel, and the detection signal output terminals of all voltage detection modules are connected with the controller of the two-way interactive electric spring; the current detection module is connected with the critical load module and the non-critical load module and the power grid transmission line in series, the output terminals of the detection signals of all current detection modules are connected with the controller of the bidirectional interactive electric spring; the phase detection module is connected with the output signals of all voltage detection modules and all current detection modules, and the detection output is connected with the bidirectional The controller of the interactive power spring is connected.

At the same time, an operation method of an interactive voltage stabilizing system with bidirectional energy flow is provided.

The effect of the present invention is that the system provides a bidirectional energy flow between critical loads and critical loads, which can increase the utilization rate of new energy power generation by 30%, and is low in cost, without additional communication, which is beneficial to the micro energy generation of new energy generators. Large-scale popularization of the grid.

(1) The present invention compensates the voltage at both ends of the critical load through the bidirectional energy flow between the critical load and the non-critical load. Compared with the traditional method, this bidirectional interactive electric spring can be used with any critical load and non-critical load The critical loads are connected in series to provide a distributed voltage control strategy to make the voltage control of critical loads more accurate and faster. Since the energy compensated for critical loads comes directly from non-critical loads, there is no need for additional energy storage devices to provide energy intermediaries, which can avoid frequent charging and discharging and greatly reduce costs.

(2) The present invention can directly compensate active power and reactive power to key loads, and the two-way interactive electric spring can provide a wider adjustment range. Compared with pure reactive power compensation measures, the device can reduce the compensation voltage. rms, reducing device stress. Since the voltage is directly compensated to the critical load, the device does not need the line impedance to share the additional voltage drop when adjusting the voltage, and does not depend on the impedance value and impedance angle of the line impedance. At the same time, it can provide voltage with any phase angle and effective value to the critical load, and the device can adjust the frequency of the voltage at both ends of the critical load.

Description of drawings

Fig. 1 is the structural diagram of the system where the voltage stabilizing system of the power grid voltage fluctuation of the present invention is located;

Fig. 2 is the internal structural diagram of the voltage stabilizing system of the power grid voltage fluctuation of the present invention;

Fig. 3 is the structural diagram of the bidirectional buck-boost DC-DC conversion circuit of the voltage stabilizing system of the energy-saving grid voltage fluctuation of the present invention;

Fig. 4 is the position and connection diagram of each detection module of the present invention;

Fig. 5 is a work flow chart of the present invention;

Fig. 6 is the structural diagram when the present invention does not work or breaks down;

Fig. 7 is a working principle diagram of the present invention when the grid voltage is lower than the reference voltage;

Fig. 8 is a working principle diagram of the present invention when the grid voltage is higher than the reference voltage.

In the picture:

1. Power grid 2. Impedance of transmission lines 3. Non-critical load modules 4. Critical load modules

5. Transmission line 6. Two-way interactive electric spring 7. Filter capacitor 8. Switching circuit

9. Controller 10. Relay 11. LC low-pass filter 12. Full bridge controllable circuit

13. Bidirectional buck-boost DC-DC conversion circuit 14. Large filter capacitor 15. Current detection module

16. Voltage detection module 17. Phase detection module

detailed description

The interactive voltage stabilizing system and operation method for bidirectional energy flow of the present invention will be described in conjunction with the accompanying drawings.

As shown in Figure 1, the voltage stabilizing system of the energy-saving grid voltage fluctuation of the present invention, the voltage stabilizing system is connected on the grid 1, and the voltage stabilizing system includes a critical load module 4, a non-critical load module 3, A two-way interactive electric spring 6, a plurality of voltage detection modules 16, a plurality of current detection modules 15, and a phase detection module 17, the two-way interactive electric spring 6 is connected in series 3 with the critical load module 4 and the non-critical load module, Connect to the grid 1 through the transmission wire 5; the capacitance of two low-pass LC filters 11 of the voltage detection module 16 and the critical load module 4, the non-critical load module 5, the power supply grid 1, and the two-way interactive electric spring 6 7 and the large capacitor parallel connection 14 of the two-way interactive electric spring, the detection signal output terminals of all detection modules are connected with the controller of the two-way interactive electric spring 9; the current detection module 15 is connected with the critical load module 4 and the non-critical load Module 3 and power grid transmission line are connected in series 5, and the output terminals of the detection signals of all detection modules are connected with the controller of bidirectional interactive electric spring 9; the output signals of the phase detection module 17 and all voltage detection modules 16 and all current detection modules 15 Connected, the detection output is connected with the controller 9 of the bidirectional interactive electric spring.

The bidirectional interactive electric spring includes two full-bridge controllable circuits 12 connected to each other, two bidirectional buck-boost DC-DC conversion circuits 13, two LC low-pass filters 11, two relays 10, a filter capacitor 14 and a controller 9, the two ends of the filter capacitor are connected to the high-voltage terminals of two bidirectional buck-boost DC-DC conversion circuits 13, and the low-voltage terminals of the two bidirectional buck-boost DC-DC conversion circuits 13 are respectively connected to The DC sides of the two full-bridge controllable circuits 12 are connected, and the AC sides of the two full-bridge controllable circuits 12 are respectively connected with two LC low-pass filters 11, and the capacitances of the two LC low-pass filters 11 are respectively connected with the critical The load module 4 and the non-critical load module 3 are connected in series and connected to the power grid 1 through the transmission line 5, and two relays 10 or switch breakers are respectively connected in parallel to the two ends of the capacitor 7 of the two low-pass LC filters.

The non-critical load module 3 includes multiple parallel loads that are not affected by voltage fluctuations.

The critical load module 4 includes multiple loads connected in parallel that require high stability of the working voltage.

Non-critical loads refer to loads that are not affected by voltage fluctuations, common non-critical loads such as water heaters, air conditioners, etc. Critical loads refer to loads that require high voltage stability, common critical loads such as computers, ECG monitors, etc.

Two relays 10 are connected in parallel with the capacitance of the LC low-pass filter 10. When the two-way interactive electric spring is not required to work or when the two-way interactive electric spring fails, the two-way interactive electric spring is short-circuited through the relays 10.

As shown in Figure 2, the bidirectional interactive electric spring includes two LC low-pass filters 11, two bidirectional buck-boost DC-DC conversion circuits 13, two full-bridge controllable circuits 12, two relays 10, a large Capacitor 14 and a controller 2. The controller controls the operation of the switching tube by outputting PWM to control the voltage effective value and phase of the capacitor 7 on the low-pass filter 11 .

The two full-bridge controllable circuits 12 in the bidirectional interactive power spring can work in rectification mode and inverter mode, and the corresponding bidirectional buck-boost DC-DC conversion circuit can work in boost mode and buck mode.

As shown in Figure 3, the bidirectional buck-boost DC-DC conversion circuits 13 connected to the two full-bridge controllable circuits 12 work in boost mode and buck mode respectively, and are used to transfer energy from one side to the other. side.

As shown in Figure 4, the voltage detection module 16 respectively detects the voltage of the power grid 1, the voltage across the critical load module 4, the voltage across the non-critical load module 3, and the two LC low-pass filters 11 of the two-way interactive electric spring 6 The effective value of the voltage at both ends of the capacitor is passed back to the controller 9 of the two-way interactive electric spring, and the voltage detection module 16 is connected in parallel to the load or power supply to detect the voltage, and the detected output is connected to the controller of the two-way interactive electric spring 9 connected.

As shown in Figure 4, the current detection module 15 respectively detects the effective value of the current on the grid transmission line 5, the current of the non-critical load module 3, and the current of the critical load module 4 and sends back to the controller 9 of the bidirectional interactive electric spring The current detection module 15 is connected in series in the circuit through which the current is to be detected, and the output terminal of the detection is connected to the controller 9 of the bidirectional interactive electric spring.

As shown in Figure 4, the phase detection module 17 respectively detects the grid voltage, the transmission line current, the current of the critical load module 4, the voltage at both ends of the non-critical load module 3, the current of the non-critical load module 3, the two-way interactive electric spring The phase difference between the voltage at both ends of the capacitor 7 of the two LC low-pass filters 11 and the voltage at the two ends of the critical load module 4 is sent back to the controller 9 of the two-way interactive electric spring, and the input terminal of the phase detection module 17 is related to all voltages, The output end of the current detection module 15 is connected to compare the phase difference between the input currents or voltages, and the detected output end is connected to the controller 9 of the bidirectional interactive electric spring.

As shown in Figure 5, the control strategy for different grid voltage conditions includes the grid 1 voltage is lower than the reference voltage, the grid 1 voltage is higher than the reference voltage, and the grid voltage is equal to the reference voltage.

As shown in Figure 5, the working principle of the interactive voltage stabilizing system of bidirectional energy flow: (1) by controlling the effective value and phase compensation of the output voltage of the capacitor of the LC low-pass filter 11 connected in series with the critical load module 4 The voltage at both ends of the critical load module 4 stabilizes the frequency and effective value of the voltage at both ends of the critical load module. (2) Compensate the excess power on the critical load 4 side to the non-critical load 3 or absorb power from the non-critical load 3 side to the critical load 4 through the bidirectional energy path inside the bidirectional interactive electric power spring 6, thereby Grid voltage fluctuations are diverted to non-critical loads3.

The two full-bridge controllable circuits 12 are used to rectify the voltage on the AC side to DC or invert the voltage on the DC side to AC. The up-down DC-DC conversion circuit 13 is used to realize the bidirectional conversion of the DC voltage, store the rectified voltage in the capacitor after boosting, or invert and output the voltage of the capacitor after stepping down. The large capacitor 14 in the middle is used for temporary energy storage and filtering. Realize the two-way transmission of energy. That is: rectifying and absorbing energy from one side and inverting the output on the other side.

The steps of the operation method of the interactive voltage stabilizing system of the two-way energy flow of the present invention are as follows:

A): The instability of new energy power generation causes the voltage fluctuation of the grid 1; the voltage detection module 16 detects the voltage change of the grid and sends it back to the controller 9 of the bidirectional interactive electric spring.

B): The controller 9 of the bidirectional interactive power spring compares the grid voltage and the reference voltage, and determines the two full-bridge controllable circuits 12 and the two buck-boost DC-DC conversion circuits 13 in the bidirectional interactive power spring 6 Working mode, if the grid voltage is lower than the reference voltage, the full-bridge controllable circuit 12 connected to the non-critical load module works in the rectification mode, and the bidirectional buck-boost DC-DC conversion circuit 13 connected to the full-bridge controllable circuit works In the boost mode, the full-bridge controllable circuit 12 connected to the key load module 4 works in the inverter mode, and the bidirectional buck-boost DC-DC conversion circuit 13 connected to the full-bridge controllable circuit works in the step-down mode; If the voltage of the grid 1 is higher than the reference voltage, the full-bridge controllable circuit 12 connected to the critical load module 4 works in the rectification mode, and the bidirectional buck-boost DC-DC conversion circuit 13 connected to the full-bridge circuit works in the boost mode , the full-bridge controllable circuit 12 connected to the non-critical load module 3 works in the inverter mode, and the bidirectional buck-boost DC-DC conversion circuit 13 connected to the full-bridge controllable circuit works in the step-down mode.

C): The controller 9 of the bidirectional interactive electric spring adjusts the phase and duty cycle of the output PWM control signal according to the voltage, current and phase difference of the critical load module 4 until the voltage at both ends of the critical load module 4 stabilizes at Reference voltage value.

As shown in FIG. 6 , when the grid voltage is equal to the reference voltage or one side of the two-way interactive electric spring fails, the two-way interactive electric spring is short-circuited through the relay 10 or the switch breaker.

As shown in Figure 5 and Figure 7, when the grid voltage is lower than the reference voltage, the full-bridge controllable circuit 12 connected in series with the non-critical load module 3 works in a rectification state, absorbing energy, so that the non-critical load module 3 two ends The voltage drops. The full-bridge controllable circuit 12 connected in series with the key load module 4 inverts and releases energy, so that the voltage at both ends of the key load module 4 increases to realize voltage compensation and power compensation.

As shown in Figures 5 and 8, when the voltage of the power grid 1 is higher than the reference voltage, the full-bridge controllable circuit 12 connected in series with the critical load module 4 works in a rectification state to absorb energy, reducing the voltage across the critical load module 4 , the full-bridge controllable circuit 12 connected in series with the non-critical load module 3 works in an inverter state to release energy, so that the voltage at both ends of the non-critical load module 3 is increased, and the voltage at both ends of the critical load is stabilized

The control over the overvoltage and undervoltage of the power grid is equivalent to transferring the fluctuation of the voltage of the power grid 1 to the non-critical load 3 to stabilize the voltage of the critical load 4 . The two-way interactive electric spring structure can also realize frequency correction of the voltage at both ends of the critical load 4 through voltage and phase compensation.

The relevant mathematical model of the two-way interactive electric spring is as follows:

Grid voltage vector

Transmission line current

reference voltage

non-critical load current

Voltage of two-way interactive power springs in series with non-critical loads

Voltage of two-way interactive power springs in series with critical loads

critical load current

Solvability of the system of equations:

There are four variables in the mathematical model: Corresponding to the four equations, four solutions on the complex domain can be obtained. So the system of equations is solvable. That is: the voltage of the critical load is controllable.

Through two-way energy transmission, the adjustment of the key load 4 voltage and the compensation of active and reactive power do not require additional energy storage devices, which can avoid frequent charging and discharging and save costs. At the same time, it can provide voltage and phase angle compensation to realize frequency correction. Since the voltage compensation is directly provided to the critical load, the dependence on the line impedance 2 is low, and there is no need for the line impedance 2 to provide an excessively high voltage division to avoid unnecessary loss. A relay 10 or a switch breaker is connected in parallel on the two-way interactive electric power spring 6 to reduce the impact of the two-way interactive electric spring on the power supply of the grid 1 under fault conditions. The invention can provide an efficient distributed voltage control strategy and an energy compensation strategy, and is beneficial to large-scale grid connection of renewable energy power generation.

Claims (5)

1. a kind of voltage-stabilizing system for adjusting voltage ripple of power network, the voltage-stabilizing system is connected on power network, it is characterized in that：The voltage stabilizing System includes key load blocks, nonessential load blocks, two-way mutual electric power spring, a Duo Ge electricity Detection module, multiple current detection modules, multiple phase detecting modules are pressed, the two-way mutual electric power spring is born with key Module and non-critical loads block coupled in series are carried, power network is connected to by transfer wire；The two-way mutual electric power spring is with closing Linked after key load blocks and the series connection of nonessential load blocks by transfer wire with power network；The voltage detection module with Key load blocks, nonessential load blocks, line voltage, two low pass LC filters of two-way mutual electric power spring Electric capacity and two-way mutual electric power spring bulky capacitor it is in parallel, the detection signal output part and two-way interactive of all detection modules The controller of formula electric power spring is connected；The current detection module and key load blocks, nonessential load blocks and electricity Net transmission line is connected, and the output end of the detection signal of all detection modules is connected with the controller of two-way mutual electric power spring； The phase detecting module is connected with the output signal of all voltage detection modules and all current detection modules, detection output with The controller of two-way mutual electric power spring is connected.

2. the voltage-stabilizing system of voltage ripple of power network is adjusted according to claim 1, it is characterized in that：The two-way mutual electric power Spring includes two full-bridge controlable electric currents of interconnection, two Bidirectional up-downs and presses DC-DC transfer circuit, two LC low Bandpass filter, two relays, a filter capacitor and a controller, the two ends of the filter capacitor and two Bidirectional up-downs Press the high-pressure side connection of DC-DC transfer circuit, the low-pressure end of two Bidirectional up-downs pressure DC-DC transfer circuit respectively with The DC side of two full-bridge controlable electric currents is connected, and the AC of two full-bridge controlable electric currents connects with two LC low pass filters respectively Connect, the electric capacity of two LC low pass filters respectively with key load blocks and non-critical loads block coupled in series, and pass through transmission Line is connected to power network, electric capacity two ends difference two relays in parallel or switch disconnector of two low pass LC filters.

3. the voltage-stabilizing system of voltage ripple of power network is adjusted according to claim 1, it is characterized in that：The nonessential load mould Block includes multiple loads not influenceed by voltage pulsation in parallel.

4. the voltage-stabilizing system of voltage ripple of power network is adjusted according to claim 1, it is characterized in that：The key load blocks Include the high load of multiple stability requirements in parallel to operating voltage.

5. using the operating method of the voltage-stabilizing system of regulation voltage ripple of power network described in claim 1, it is characterized in that：This method is grasped It is as step：

A)：The unstability of generation of electricity by new energy causes voltage ripple of power network；Voltage detection module detects grid voltage change simultaneously Pass the controller of two-way mutual electric power spring back；

B)：The controller of two-way mutual electric power spring compares line voltage and reference voltage, and determines two-way mutual electric power The mode of operation of two full-bridge controlable electric currents and two step-up step-down DC-DC translation circuits in spring, if line voltage Less than reference voltage, the full-bridge controlable electric current being connected with nonessential load blocks is operated in rectification mode, can with the full-bridge The Bidirectional up-down pressure DC-DC transfer circuit of control circuit connection is operated in boost mode, is connected with key load blocks Full-bridge controlable electric current is operated in inverter mode, the Bidirectional up-down pressure DC-dc conversion electricity being connected with the full-bridge controlable electric current Road is operated in decompression mode；If line voltage is higher than reference voltage, the full-bridge controlable electric current being connected with key load blocks Rectification mode is operated in, the Bidirectional up-down pressure DC-DC transfer circuit being connected with the full-bridge circuit is operated in boost mode, with The full-bridge controlable electric current of nonessential load blocks connection is operated in inverter mode, the two-way liter being connected with the full-bridge controlable electric current Decompression DC-DC translation circuit is operated in decompression mode；

C)：The controller of the two-way mutual electric power spring is adjusted according to the voltage, electric current and phase difference of key load blocks The phase and dutycycle of section output pwm control signal, until the voltage stabilization at key load blocks two ends is in reference voltage level.