CN116316664A

CN116316664A - Method and device for treating voltage sag of parallel active power filter based on super capacitor

Info

Publication number: CN116316664A
Application number: CN202111473207.7A
Authority: CN
Inventors: 卢浩; 任建功; 朱辉; 朱翌
Original assignee: Suzhou Sifang Zhidian Energy Technology Co ltd
Current assignee: Suzhou Sifang Zhidian Energy Technology Co ltd
Priority date: 2021-12-06
Filing date: 2021-12-06
Publication date: 2023-06-23

Abstract

The invention discloses a method and a device for treating voltage sag of a parallel active power filter based on a super capacitor. The device comprises: the device comprises a super capacitor, an active power filter, a voltage sag detection module and a bidirectional thyristor module. The super capacitor is connected with the direct current side of the active power filter, when the power grid is normal, the active control function is utilized to charge and constant voltage the super capacitor, the switch K1 is in a bypass state, and the bidirectional thyristor is in a conducting state. When voltage sag occurs, the detection device sends out a grid-connected off-grid switching and thyristor enabling prohibition instruction. The active power filter receives the instruction, turns off the thyristor, and converts the off-grid voltage source mode into the off-grid voltage source mode to provide short-time power supply for the load. After the power grid is recovered to be normal, the voltage sag detection module sends an off-grid-to-grid instruction, and sends the amplitude and the phase of the power grid to enable the thyristor to be switched on, and the active power filter recovers to be in a grid-connected mode. The device realizes short-time voltage sag control in the mode, and has the advantages of simple structure, small volume and low cost.

Description

Method and device for treating voltage sag of parallel active power filter based on super capacitor

Technical Field

The invention relates to the technical field of electric power, in particular to the aspect of voltage sag protection.

Background

Voltage sag is a common fault of factory power supply, and is caused by short-time and large-scale change of voltage amplitude caused by lightning stroke, large-scale load switching, equipment short circuit and other events. The consequences that result typically include malfunction of the device, or operation within a limited range, and in severe cases the device is inoperable. More seriously, the process flow is started to have a continuous effect. The evaluation of the voltage dip depends on the dip amplitude and duration. According to the statistical data of the voltage sag in the United states, the amplitude of the sag is up to 0.7pu-0.9pu with the proportion of 70 percent, the duration is not more than 0.1s with the proportion of 60 percent, and the average number of times of the whole year is 56 times.

Aiming at the problem of grid sag, the main solution is to configure a dynamic voltage regulator, which is coupled through a transformer and connected in series between a power grid and a load, and compensates for voltage loss in real time in a grid-connected mode. The whole machine topology adopts a transformer and a back-to-back inverter, the compensation voltage sag depth is from 0.9pu to 0.3pu, no requirement is required for duration, and the device is commonly applied to the chip manufacturing industry.

The conventional equipment has problems in that its cost and selling price are high. And for the common nonlinear load and the three-phase unbalanced load, the loss is multiplied by the compensation of the transformer. It is generally difficult for small and medium-sized electricity consumers to accept high selling prices and high losses. The active power filter is specially used for managing harmonic components in grid current and is a commonly used electric energy quality management product. The invention is improved by a low-cost scheme, has the function of treating voltage sag, and has the significance of continuously stabilizing voltage and improving product quality for power supply of sensitive loads of factories.

Disclosure of Invention

The invention aims to provide a device and a method for arranging auxiliary power grid sag, which are specially used for treating power grid faults with voltage sag amplitude values of 0.9pu-0.7pu and duration time less than 0.1s, and have the advantages of small volume, low cost and wide application occasions.

The invention provides a super capacitor-based parallel active power filter voltage sag control device, which comprises: and the super capacitor is connected to the direct current side of the active power filter and used for storing energy output by the voltage sag.

The active power filter works in a working state of compensating reactive power or compensating harmonic waves in daily life, when voltage is subjected to sag, the energy of the direct-current super capacitor is converted into load power supply in a voltage source mode through a seamless grid-connection and grid-disconnection technology, and when a power grid is recovered to be normal, the power grid is switched to the power grid in a seamless mode.

The voltage sag detection device is provided with a sampling point which is arranged at the power grid side, and provides a voltage switching instruction and a parallel-off-grid switching instruction for the active power filter by detecting the amplitude and the phase of the power grid voltage; meanwhile, the super capacitor detection device is capable of detecting the state of the super capacitor and timely early warning overvoltage and overtemperature faults.

The bidirectional thyristor module is used as a seamless grid-connected to-off grid switch between a power grid and a load and is connected in parallel with the load power supply circuit breaker, and when the equipment is put into operation, the load power supply circuit breaker is disconnected, and the thyristor is in a conducting working state; when voltage sag occurs, the bidirectional thyristor module is actively turned off, and the active power filter is converted into an off-grid working mode to supply power to a load.

A super capacitor is added on the direct current side of an active power filter to serve as energy storage equipment, a series bidirectional thyristor is connected between a power grid and a load in series to serve as a grid-connected to grid-off seamless switch, the active power filter is directly converted into a voltage source to supply three-phase four-wire power, and at the moment, the active power filter and the power grid are in parallel connection. The length of time that the load is powered depends on the energy configuration of the supercapacitor. The average number of times per year is 56 times because of the statistics of the voltage sag in the united states, the sag amplitude is up to 0.7pu-0.9pu with a 70% ratio, the duration is not more than 0.1s with 60%. For the occasion that the serial dynamic voltage regulator is not required to be added, but the requirements of improving the product quality and the power supply quality are met, the invention has the significance of high cost performance and high return.

Two types of equipment for compensating voltage sag are compared, wherein the first type is to raise the terminal voltage by injecting capacitive reactive power; the second is to compensate the voltage sag part of the power grid through transformer coupling. The first mode is to inject reactive lifting voltage, occupy power grid capacity, and is easy to oscillate and unfavorable for stabilizing load power supply voltage, the second mode is to compensate through a series transformer, equipment cost is high, back-to-back topology inverters are needed to be provided, long-time inversion work is performed, loss is large, the number of times of power grid sag is small, time is in the order of tens of ms, and voltage compensation is only needed to be provided for specific time.

According to the invention, the energy storage device is added on the direct current side on the basis of the active power filter, charge and discharge control can be realized through the device body, the bidirectional thyristor switch is added between the power grid and the load, the power grid connection is disconnected when the power grid is in a sag, and the voltage source control is performed through the active power filter. The whole scheme is added with the energy storage element and the switching element, the isolation transformer and the charging inverter are not involved, the power grid reactive power and harmonic state compensation system works daily, the self-starting and stopping function can be set according to the power grid compensation current, the power grid sag is controlled through an internal algorithm, the grid connection state and the off-grid state are seamlessly switched, the compensation time is short, the utilization rate and the efficiency and the cost of the whole machine are greatly improved compared with those of the traditional scheme, and the power grid sag is suitable for popularization and production.

Compared with the prior art, the invention has three advantages:

first, the cost is low. The active power filter is a commonly used product, has rich application occasions, adopts conventional product materials, and has cost advantages; the traditional scheme has the advantages that the manufacturing cost is several times higher, a large-power transformer is used under the same capacity, more than twice the number of power electronic devices and twice the occupied area of the invention are adopted, the cost is difficult to reduce in principle, and the high-performance price ratio is not achieved.

Second, the response is fast. The off-grid seamless switching technology adopts the back-pressure switching-off technology for the bidirectional thyristors, the response time is within 1ms, the output is converted into a voltage source mode, and the total switching time is completed within 3 ms. The traditional technology is to extract a negative sequence component and a harmonic component through an instantaneous reactive power theory or Fourier transformation, and the compensation full response time is more than 10 ms.

Third, the loss is low. The invention has the characteristics of energy conservation by adding the voltage compensation function and daily compensation of reactive current and harmonic current on the basis of the active power filter, and compensates the voltage sag of the power grid by a seamless off-grid technology, thereby having short time and not increasing extra cost for users. The traditional technology is a long-time compensation scheme and continuously operates, so that 2% -3% of loss is brought to users, and the cost of the users is increased.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is an electrical schematic diagram of a super capacitor based parallel active power filter compensation voltage sag of the present invention;

FIG. 2 is a functional diagram of a voltage sag detection device according to the present invention;

FIG. 3 is a method of voltage sag detection of the present invention;

FIG. 4 is a flow chart of the grid-connected to off-grid switching of the present invention;

FIG. 5 is a flowchart of off-grid to on-grid switching in accordance with the present invention;

FIG. 6 is an algorithmic structure in the active power filter compensation state of the present invention;

FIG. 7 is an algorithmic structure of an active power filter turn-off thyristor of the invention;

FIG. 8 is an algorithmic structure of the off-grid operation of the active power filter of the present invention;

fig. 9 is an electrical schematic of a dynamic voltage restorer.

Detailed Description

The invention is described in further detail below with reference to the drawings and examples. It is specifically noted that the following examples are only for illustrating the present invention, but do not limit the scope of the present invention. Likewise, the following examples are only some, but not all, of the examples of the present invention, and all other examples, which a person of ordinary skill in the art would obtain without making any inventive effort, are within the scope of the present invention.

As shown in FIG. 1, the super capacitor-based parallel active power filter manages voltage sag, and comprises a power grid sag detection device, a bidirectional thyristor module, an active power filter, a super capacitor module, a switch K1, a switch K2, power grid current sampling, off-grid switching control and thyristor control.

In the electrical schematic diagram, a power grid sag detection device, a bidirectional thyristor module, a super capacitor module, off-grid switching control and thyristor control are added on the basis of reactive power and harmonic wave treatment of an active power filter.

For the usual functions of the active power filter, the algorithm framework is described with reference to fig. 6.

The switch K1 is a power supply breaker of a load, two sides of the switch are connected with bidirectional thyristor modules in parallel, the bidirectional thyristor modules are used for fast switching when voltage sags, and the bidirectional thyristor is conducted to supply power to the load when the device works normally. The switch K1 functions as a bypass switch, and when the device is maintained, the switch K1 is closed to supply power to the load.

The switch K2 is an external breaker of the active power filter and is used for being connected with the main loop in parallel, and under the condition that the device has a short-circuit fault, the switch is tripped, and the device is isolated from a power grid.

The super capacitor is used for manufacturing the energy storage element, has the characteristics of short-time high-rate charge and discharge, high power density, wide working temperature, no need of maintenance, good series-parallel voltage equalizing effect, 60% of event with duration time lower than 0.1s in the power grid sag characteristic, and the high-power discharge characteristic of the super capacitor in short time, and is an excellent choice for providing energy in the power grid sag.

The active power filter is composed of three half-bridge arms, wherein the middle point of the active power filter is led out and connected with N lines, the common system is a three-phase four-wire system, three single-phase bridge circuits are equivalent, and the compensation algorithm is a single-phase control strategy, so that the active power filter has good effect of compensating reactive power and harmonic waves in a three-phase unbalanced state. The topology and algorithm are also suitable for providing power supply voltage for three-phase four-wire system loads in off-grid mode.

The power grid sag detection device is based on the principle that the occurrence of sag is judged by sampling power grid voltage and a voltage sag algorithm, the depth and duration of the power grid sag are recorded, and a grid-connected to-off-grid instruction and a grid-off-grid to-grid instruction are provided for an active power filter, so that the power grid sag detection device is a core module of the power grid sag detection device. In addition, the power grid sag detection device also controls the on and off of the thyristors, sends power grid side amplitude and phase information through communication with the active power filter CAN, and receives the working mode and state of the active power filter.

The bidirectional thyristor is used as a switch for rapidly switching a power supply, the type selection notes are respectively high-rate overload and working voltage ranges, the high-rate overload parameter is mainly applied to overload tolerance capacity under the condition of load short circuit, and the working voltage range parameter is mainly based on the highest value of the voltage peak of the thyristor at the moment of turn-off. Because the thyristors are loaded for a long time, the thyristor unit modules are designed, and the design of the cooling fins and the air channels should be considered.

As shown in fig. 2, the power grid sag detection device internally comprises a power grid voltage sampling circuit board, a super capacitor CAN communication interface 1, an active power filter CAN communication interface 2, two DO ports special for off-grid switching, one pre-warning DO port in a super capacitor fault state and one thyristor control enabling signal.

The power grid voltage sampling circuit board collects power grid phase voltage instantaneous values, analog-to-digital signals are converted into discrete values between 0 and 4096 through a CPU chip integrated ADC (analog-to-digital converter) of the power grid sag device, and then the power grid phase voltage is restored into an actual value through zero offset and band coefficient conversion.

Two algorithms are integrated in the CPU of the power grid sag detection device, and a power grid amplitude and phase algorithm and a self-grinding voltage sag judgment algorithm are detected. The former performs a clark conversion and a park conversion on the grid phase voltage, and converts three alternating current components in a three-phase static coordinate into two direct current components in a two-phase rotating coordinate, wherein a D-axis component represents the grid voltage amplitude, and a Q-axis component represents the grid voltage phase. And carrying out phase-locking control through a voltage Q axis to obtain the electric angle theta of the power grid. The power grid sag detection device sends the calculated amplitude and the calculated power grid electrical angle to the active power filter through CAN communication once every 1 ms.

As shown in fig. 3, if the D-axis component of the power grid represents the amplitude, when the power grid generates a symmetrical or asymmetrical voltage sag, and the sag amplitude is smaller than 0.9pu, the CPU starts a sag depth and delay matching algorithm to confirm that the power grid sag occurs. The method is used for avoiding occurrence of an event of misjudgment of occurrence of the grid sag caused by voltage spike caused by heavy load switching. And after confirming that the grid sag occurs, the grid sag device sends a grid-connected to off-grid switching DO signal to the active power filter, and informs the active power filter of carrying out the next mode switching.

At the same time, the grid sag detection device sends out a signal for prohibiting the enabling of the thyristor, and the thyristor driving circuit stops sending out the trigger level. If no other action is applied, the bidirectional thyristor will be in a state of natural back-pressure turn-off, and the maximum time will be 10ms for back-pressure turn-off. This is contrary to the concept of fast switching, nor is the load able to withstand short-term low voltage fluctuations.

As shown in fig. 4, the active power filter will automatically complete the switching from the grid-connected state to the off-grid state. In this embodiment, the active power filter plays the role of turning off the thyristor, which is turned off rapidly within 1ms by actively outputting a reverse voltage. The algorithm structure of the output back voltage of the active power filter is shown in fig. 7, and the back voltage higher or lower than the end voltage of the thyristor is rapidly output by directly superposing the reverse voltage to the feedforward voltage, which needs to be explained here, because the bidirectional thyristor is adopted, the thyristor is in what kind of on state, and the output back voltage of the active power filter is determined to be positive or negative by jointly judging the direction of the power grid voltage and the power grid current.

The active power filter samples a power grid side current signal to be used as a compensation current calculation setting, and in the back voltage turn-off process, the active power filter can complete the basis of turning off the thyristor by sampling the value of the power grid current. When the current of the power grid is smaller than a certain value and the level of hundred us is maintained for a long time, the active power filter judges that the bidirectional thyristor is completely disconnected, and the load is isolated from the power grid. The active power filter is switched to an off-grid state, three-phase power supply voltage is directly output, the algorithm structure is shown in fig. 8, and the active power filter can complete establishment of steady-state voltage within 2 ms. The service time of the comprehensive breaking thyristors is 1ms at most, and the active power filter completes switching from a grid-connected state to an isolated off-grid state within 3 ms.

As shown in fig. 5, the active power filter will cooperate with the signal of the voltage sag detection device to complete the switching from the off-grid state to the on-grid state. The voltage sag detection device monitors the amplitude and the phase of the power grid which are recovered to be normal, sends a switching instruction for switching from off-grid to on-grid to the active power filter, and continuously sends the voltage amplitude and the power grid electrical angle information at the power grid side through CAN communication.

The active power filter is controlled by an internal synchronization algorithm, synchronization of the amplitude and the phase angle of the power grid voltage is completed within 10ms, the amplitude and the phase angle meet the conditions after synchronization, and a grid-connected instruction is fed back to the voltage sag detection device through CAN communication. The voltage sag device sends out a thyristor-enabled driving signal and directly communicates back to the grid-connected instruction.

After receiving the grid-connected instruction, the active power filter firstly blocks PWM, exits from the grid-connected state, and is converted into grid-connected mode control, and reactive power and harmonic waves of the power grid are compensated in a soft start mode.

The active power filter is matched with the biphase thyristor module through the power grid sag detection module, compensation work under the power grid sag fault is completed, and the active power filter is used for completing work of supplementing electric energy to the super capacitor on the basis of not affecting the power supply capacity through a direct-current voltage soft recovery mode.

Compared with the closest prior art, the technical scheme provided by the invention has the following characteristics and effects: compared with a dynamic voltage restorer, as shown in fig. 9, the invention reduces the use of a trimming module and a series transformer, increases a super capacitor module, and has smaller overall volume and lower cost than the latter.

And (3) for the power grid fault working condition that the voltage sag amplitude is as low as 0.7pu and the duration is not longer than 0.1s, the active power filter is pertinently modified to have the compensation function of the voltage sag. The compensation principle of the active power filter is also applicable to power grid fault conditions exceeding the voltage sag amplitude, and the active power filter is matched as required by increasing the capacity of the super capacitor for power grid fault conditions with the duration of sag exceeding 0.1 s. For general application occasions, the working condition that the power grid sag exceeds 0.1s, the number of occurrences in one year is single, the cost brought by the super-capacitance configuration is increased, and the configuration can be selected as appropriate.

The invention comprises hardware such as a voltage sag detection module main controller, an active power filter main controller, a bidirectional thyristor drive current, a power grid voltage sampling circuit, a communication circuit, an optocoupler circuit and the like, and also comprises software such as voltage and current double closed-loop control loops, off-grid switching control logic, back voltage output, thyristor turn-off detection algorithm, communication and the like.

Those of ordinary skill in the art will appreciate that: the above discussion of the embodiments is exemplary, but is not intended to illustrate that the scope of the disclosure is limited to this embodiment, and the technical features of the above embodiments may be combined or integrated into the same functional module, where many variations exist in different implementations of the invention, and not provided in detail for brevity.

In addition, in order that the invention may be readily understood, hardware-related is not shown in the drawings, and since there are many different forms of hardware implementations, this example merely illustrates the implementation, and these descriptions should be considered illustrative for the purposes of understanding the details of implementations to those skilled in the art.

The embodiments of the invention are intended to embrace all such alternatives, modifications and variances which fall within the broad scope of the appended claims. Therefore, any omission, modification, equivalent replacement, improvement, etc. of the present invention should be included in the scope of the present invention.

Claims

1. A super capacitor-based parallel active power filter voltage sag control device is characterized by comprising: the device comprises a voltage sag detection device, a bidirectional thyristor module, a super capacitor, an active power filter and a bypass switch K1, wherein the voltage sag detection device is used for detecting power grid sag and recovery and has the functions of enabling and disabling the bidirectional thyristor, power grid information interaction is carried out through CAN communication and the active power filter, off-grid seamless switching instructions are completed, the super capacitor is monitored on line through CAN communication, the bidirectional thyristor module is used for rapidly disconnecting a load from a power grid at the moment of power grid sag, the voltage sag device is used for disabling bidirectional thyristor driving, the active power filter outputs reverse voltage to rapidly switch off the thyristor, and ms-level separation capacity is achieved.

2. The super capacitor-based parallel active power filter voltage sag control device as set forth in claim 1, wherein the voltage sag detection device comprises a voltage sampling circuit and a CPU processor.

3. The super capacitor-based parallel active power filter voltage sag control device according to claim 1, wherein the voltage sag detection device comprises a liquid crystal screen.

4. The device for managing voltage sag of the super capacitor-based parallel active power filter according to claims 1 and 2 is characterized in that the voltage sag detection device has the functions of detecting voltage sag, recording wave, calculating sag depth and duration, requesting the active power filter to record load supply voltage through CAN communication, completing the recording of load supply voltage before and after compensation, and displaying compensation effect through a liquid crystal screen.

5. The super capacitor-based parallel active power filter voltage sag control device is characterized in that the active power filter receives a grid-connected to grid-off DO instruction, a grid-off to grid-connected DO instruction and an alarm instruction of a voltage sag detection device through three dry nodes.

6. The super capacitor-based parallel active power filter voltage sag control device according to claim 1, wherein the active power filter receives power grid side voltage amplitude and voltage phase information, thyristor enabling and disabling information of the voltage sag detection device through CAN communication.

7. The device for controlling voltage sag of the parallel active power filter based on the super capacitor as claimed in claim 1, wherein the active power filter is used for rapidly outputting reverse turn-off voltage of the thyristor in a mode of actively turning off the bidirectional thyristor by superposing feedforward voltage on reverse voltage.

8. The super capacitor-based parallel active power filter voltage sag control device according to claim 1, wherein the active power filter detects power grid side current information, and the reverse voltage output direction is selected by reversing power grid voltage and power grid current.

9. The super capacitor-based parallel active power filter voltage sag control device is characterized in that the active power filter has an off-grid function and can output constant-frequency and constant-voltage power supply voltage.