CN111564896B - Smooth switching and flexible exiting method and device for voltage sag control device - Google Patents
Smooth switching and flexible exiting method and device for voltage sag control device Download PDFInfo
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Abstract
The invention relates to a smooth switching and flexible exiting method and a device of a voltage sag treatment device, when an energy storage converter operates from a grid-connected mode to an off-grid mode, a voltage control loop in a control strategy enables the energy storage converter to output voltage which is the same as the load voltage before sag, and commercial power is cut off from a power grid by matching with a thyristor gate control signal to complete the smooth switching of the commercial power to the energy storage converter; when the energy storage converter is switched from an off-grid mode to a grid-connected mode, the voltage of the energy storage converter and the voltage of a power grid are synchronized through a voltage control loop and an automatic synchronization control loop in a control strategy, a thyristor is triggered to be conducted, the current of the energy storage converter is controlled in a slow step mode to be reduced to the current of the energy storage converter during grid connection, and the conversion of the energy storage converter and the power grid line is completed; and when the active power and the reactive power output by the energy storage converter are respectively smaller than the threshold value, the energy storage converter is flexibly withdrawn. The invention realizes high-quality electric energy supply to the sensitive load before and after the temporary drop, and avoids the energy storage converter providing great impact current to the sensitive load.
Description
Technical Field
The invention relates to the field of smooth switching and flexible exiting of a voltage sag treatment device, in particular to a voltage sag treatment device smooth switching and flexible exiting method and device based on a voltage type control strategy.
Background
Technical updating of electric equipment puts higher requirements on power supply quality, and voltage sag is one of the most serious power quality problems with the highest occurrence frequency. Particularly, short-time voltage sag can cause abnormal work of sensitive loads such as logic programmable controllers, precision mechanical tools, semiconductor production lines and the like, even equipment damage, and huge economic loss is brought to enterprises. The economic cost and the technical difficulty of the existing voltage sag control are comprehensively considered, the voltage sag control equipment is the most common voltage sag control technology for sensitive users, and the parallel voltage sag control device based on the energy storage equipment is widely applied to the field of low-voltage power distribution because of a plurality of advantages. When voltage sag and other abnormal conditions occur in a power grid, the parallel voltage sag management device based on the energy storage needs to be changed from a grid-connected working mode to an off-grid working mode to ensure the power supply reliability of sensitive users, at the moment, the energy storage device plays a main supporting role on the voltage and frequency of the sensitive users, the smooth transition of the voltage needs to be ensured in the switching process, and the voltage is prevented from sudden change.
Currently, an energy storage converter in a parallel voltage sag management device with an energy storage device generally adopts different control strategies according to different operation modes. For example, in a grid-connected operation mode, the energy storage converter generally directly uses the grid frequency and voltage as a support, and at this time, the energy storage converter operates in a current source mode. The control algorithm is called as active and reactive power PQ control, because the energy storage converter is connected with a power grid when the power grid is connected, the output voltage and the frequency of the energy storage converter are clamped by the power grid, and at the moment, if the energy storage converter is controlled, the output current of the energy storage converter can be only indirectly controlled by controlling the active and reactive power, so that the result that the output power of the energy storage converter is consistent with the set value of the power is realized; in the off-grid mode, the energy storage converter generally uses constant-voltage VF control, and the reason for selection is that when the energy storage converter operates in an off-grid mode, the energy storage converter is generally used as a power supply, so constant-voltage and constant-frequency VF control needs to be provided outwards, and the VF control can be generally divided into voltage single-loop control, voltage double-closed-loop control and voltage and current double-closed-loop control. The most common is voltage-current double closed-loop control. When a voltage sag occurs, the energy storage converter needs to switch the operation mode from PQ control to VF control, and if the mode is not properly switched, a surge voltage caused by mode switching may occur to affect the normal operation of sensitive equipment. Therefore, it is very important that the sensitive load voltage remains unchanged before and after the voltage sag, and a control strategy is needed to enable the energy storage converter to be smoothly switched when the sag occurs and to be flexibly exited after the sag occurs.
The energy storage converter is required to realize high-quality electric energy supply before and after the temporary drop of the sensitive load, improve the switching speed of the energy storage converter, avoid the energy storage converter from providing large impact current for the sensitive load and carry out smooth switching and flexible exit control on the energy storage converter.
Disclosure of Invention
The invention aims to provide a smooth switching and flexible exiting method of a voltage sag treatment device, which is suitable for various operation modes of an energy storage converter in a treatment process, realizes smooth switching of the energy storage converter from a grid-connected mode to an off-grid mode and flexible exiting of the energy storage converter from the off-grid mode to the grid-connected mode through a control method on the basis of quickly treating voltage sag, and avoids large pulse current applied to a sensitive load before and after the sag, thereby ensuring the power utilization reliability of a sensitive load user.
A smooth switching and flexible exiting method for a voltage sag treatment device comprises the following steps:
judging the working mode of the energy storage converter according to the output voltage of the energy storage converter and the voltage of a power grid, wherein the working mode comprises a grid-connected mode, an off-grid mode and an automatic synchronization mode;
when voltage sag occurs, the energy storage converter is switched from a grid-connected mode to an off-grid mode: enabling the energy storage converter to output voltage which is the same as the load voltage before the temporary drop through a voltage control loop, enabling the energy storage converter to output current to replace the current of a power grid through a power control loop and the voltage control loop, and then cutting off the commercial power from the power grid to finish smooth switching of the commercial power supply to the energy storage converter;
when the voltage sag disappears, the energy storage converter is switched from an off-grid mode to a grid-connected mode: the voltage control loop and the automatic synchronization control loop are used for synchronizing the voltage of the energy storage converter with the voltage of a power grid, then mains supply is connected into a load from the power grid, the current of the energy storage converter is controlled in a slow step mode to be reduced to the current during grid connection, conversion between the energy storage converter and a power grid line is completed, and in the process, when active power and reactive power output by the energy storage converter are respectively smaller than threshold values, the energy storage converter is flexibly withdrawn and is completely powered by the mains supply.
Further, the method also comprises the following steps: the method comprises the steps of constructing a topological circuit, wherein the topological circuit comprises an energy storage body, an energy storage converter, a first isolating switch, a second isolating switch and a thyristor, a power grid is connected with a sensitive load through the first isolating switch, the thyristor and the second isolating switch, the energy storage body and the energy storage converter are connected in series, then the output end of the energy storage body is connected between the thyristor and the second isolating switch, when the voltage of the power grid is normal, the energy storage converter is in an off-grid state, the sensitive load is powered by the power grid, and the output current of the energy storage converter is 0.
The utility model provides a voltage sag treatment device smooth switch and flexible exit device, includes that operating mode judges unit, voltage control ring, power control ring, automatic synchronization control ring:
the working mode judging unit is used for judging the working mode of the energy storage converter according to the output voltage of the energy storage converter and the voltage of a power grid, and the working mode comprises a grid-connected mode, an off-grid mode and an automatic synchronization control mode;
the voltage control loop is used for enabling the energy storage converter to output voltage which is the same as the load voltage before voltage sag when the voltage sag is judged to occur, the power control loop and the voltage control loop enable the energy storage converter to output current to replace power grid current, and then commercial power is cut off from the power grid to finish smooth switching of commercial power supply to the energy storage converter;
and the voltage control loop and the automatic synchronization control loop are used for synchronizing the voltage of the energy storage converter and the voltage of the power grid when the voltage sag disappears, then the mains supply is connected into a load from the power grid, the current of the energy storage converter is controlled to be reduced to the current during grid connection in a slow step mode, the conversion between the energy storage converter and the power grid line is completed, and in the process, when the energy storage converter outputs active power and reactive power for a certain time respectively less than a threshold value, the energy storage converter is flexibly withdrawn and is completely supplied with power by the mains supply.
Furthermore, the integral links of the PI controllers used for the power control loop, the automatic synchronization control loop and the voltage control loop are enabled or disabled by an S value, and the S value represents different working modes of the energy storage converter.
Further, the device also comprises a coordinate transformation and power calculation unit which is used for calculating the three-phase terminal voltage u output by the energy storage converter pabc Three-phase network voltage u gabc And three-phase output current i pabc Respectively obtaining the instantaneous active voltage value u output by the energy storage converter under the dq coordinate system after abc/dq coordinate transformation pd The energy storage converter outputs an instantaneous reactive voltage value u pq And the active component u of the network voltage gd Reactive component u of the grid voltage gq And three-phase output current active component i pd Three-phase output current reactive component i pd Then, instantaneous active and reactive power calculation is carried out to obtain the values of instantaneous active P and instantaneous reactive Q, and the calculation formula is as follows:
wherein the rotation angle θ for coordinate transformation is represented as follows:
θ＝∫(ω 0 +Δω+Δω syn )dt
in the formula, ω 0 Is a rated angular frequency value, delta omega is an output value of an active control part of the power control loop, and delta omega syn The output value is controlled for the q-axis component of the automatic contemporaneous control loop.
Further, the power control loop comprises an active power control loop and a reactive power control loop,
the active power control loop is used for obtaining the instantaneous active power P after the instantaneous active power P passes through a Low Pass Filter (LPF) LPF Then the active power is assigned a value P ref And P LPF Comparing, outputting delta omega value as output value of active control part of power control loop through PI controller,
the reactive power control loop is used for obtaining the instantaneous reactive power Q after passing through a Low Pass Filter (LPF) LPF Then, the reactive power is assigned to a value Q ref And Q LPF And comparing, and outputting the delta E value as the output value of the reactive part controlled by the power control loop through the PI controller.
Furthermore, the automatic synchronization control loop comprises an active component synchronization control loop and a reactive component synchronization control loop,
the active component synchronous control loop is used for controlling the active component u of the power grid voltage gd And the energy storage converter outputs an instantaneous active voltage value u pd Comparing, and outputting the difference value delta E through a PI controller syn The value is used as the output value of the active component control of the automatic synchronous control loop,
the reactive component synchronous control loop is used for converting the reactive component u of the power grid voltage gq And the energy storage converter outputs an instantaneous reactive voltage value u pq Comparing, and outputting the difference value to delta omega via PI controller syn And the value is used as the reactive component control output value of the automatic synchronous control loop.
Further, the voltage control loop comprises an active component voltage control loop and a reactive component voltage control loop,
command value of the active component voltage control loop
And instruction of reactive component voltage control loopValue->
Calculated by the following formula:
wherein, E 0 For voltage feedforward values,. DELTA.E is the reactive power control loop output value,. DELTA.E syn Controlling an output value for an active component of an automatic synchronization control loop;
active component voltage control loop for providing voltage active component command value
And a feedback value u pd Comparing, outputting U by PI controller dref A value;
the reactive component voltage control loop is used for converting the voltage reactive component instruction value
And a feedback value u pq Comparing, outputting U by PI controller qref Value of said U dref And U qref After the conversion processing of the dq/alpha beta coordinate conversion unit, the space vector pulse width modulation unit outputs the needed PWM pulse to a switch tube in the energy storage converter, and the switching and exit of each working mode are realized by controlling the on-off of the switch tube through the PWM pulse.
Compared with the closest prior art, the invention has the following beneficial effects:
(1) Compared with other voltage sag equipment and control schemes, the voltage sag control method has the advantages that the current control inner loop is reduced, the voltage synchronous control is added, and the power control loop and the voltage control loop form a unified framework, so that the energy storage converter has higher response speed in mode switching, and experimental results show that the energy storage converter can complete smooth switching within 3ms when the sag occurs.
(2) The control strategy is under a unified framework, so that the energy storage converter is more stable and stable during mode switching, the generation of impact current when the mode switching is not proper is avoided, and the reliability of power supply is ensured.
(3) The topology (voltage sag treatment equipment based on the energy storage converter) can flexibly configure energy storage capacity according to loads, can design redundant equipment, further improves fault tolerance rate, and comprehensively improves the quality of electric energy at a user side.
Drawings
FIG. 1 is a topological circuit diagram of the parallel voltage sag management device of the present invention;
FIG. 2 is a control strategy diagram of the present invention;
FIG. 3 is a schematic diagram of the flexible exit active and reactive command change of the present invention;
FIG. 4 is a flow chart of the present invention for determining the operating mode;
FIG. 5 is a flow chart of the flexible exit algorithm of the present invention;
fig. 6 (a) is an experimental waveform of the voltage sag (0.3 pu) of the present invention, and fig. 6 (b) is an experimental waveform of the voltage sag (0 pu) of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
The control strategy provided by the invention adopts a power control loop 42, an automatic synchronization control loop 43 and a voltage control loop 44 to form a unified framework as shown in fig. 2 so as to avoid the impact of the energy storage converter during mode switching, reduce the current control loop in an off-grid mode, simplify the complexity of the control strategy, shorten the mode switching duration, reduce the error during mode switching, and have better rapidity and stability.
When voltage sag occurs, a sensitive load is switched into an energy storage converter from commercial power, the energy storage converter starts to work, the energy storage converter outputs current to replace power grid current through a control strategy, the power grid current is infinitely close to zero at the moment, a gate pole signal of a bidirectional thyristor is turned off to meet the thyristor turn-off condition, the commercial power is cut off from a load loop, and the energy storage converter provides electric energy for the load.
When the voltage sag is over, the sensitive load is switched to a mains supply by the energy storage device, before the bidirectional thyristor is triggered, the alternating-current side voltage of the energy storage device and the mains supply are controlled to be synchronous, and when the alternating-current side voltage and the mains supply meet the conditions of same frequency, same amplitude and same phase, the thyristor is triggered to be conducted. After the thyristor is conducted, if the switching between the energy storage device and the mains supply is instantly completed, the switching is equivalent to a step current suddenly increased by the current output of the power grid, a large impact may be caused on the load side, and even the converter resonates, so that the protection action of the sensitive equipment or the converter is triggered, therefore, after the energy storage device completes the same period with the load, the current output by the energy storage device can be slowly reduced, the current output by the energy storage converter is reduced by the no-load current at a certain rate, and then the energy storage converter is withdrawn, so that the generation of the impact current is avoided, and the process is called flexible withdrawal.
The embodiment of the invention provides a smooth switching and flexible exit method of a voltage sag control device based on a voltage type control strategy, which is mainly used for a parallel voltage sag control device and comprises the following steps:
the step 2 specifically comprises the following steps:
step 2.1, the integration segments of the PI controllers for the three control loops (power control loop 42, voltage control loop 44, automatic synchronization control loop 43) are enabled or disabled by the S value. The S values indicate different operation modes of the energy storage converter 22, S =1 indicates that the converter operates in a grid-connected mode, S =2 indicates an off-grid mode, and S =3 indicates a synchronous mode. The control methods of different modes are integrated into one control strategy by reasonably designing the PI controller, so that the control algorithms between different modes are smoothly switched.
Taking the PI controller of the power control loop 42 as an example:
it combines PI controller and proportional controller, and the enable or disable of PI controller integral part is determined by S value. If the energy storage converter 22 is in grid-tie mode, S will be defined as S =1 and the PI controller integral part for the power control loop 42 will be immediately enabled. Meanwhile, 0 is used as an input of the integrating segments of the voltage control loop 44 and the automatic synchronization control loop 43, and at this time, the integrating portions of the PI controllers of the voltage control loop 44 and the automatic synchronization control loop 43 will fail.
Similarly, if the energy storage converter 22 is in off-grid mode, the S value will be defined as S =2, the integral part of the PI controller for the voltage control loop 44 will be immediately enabled, while 0 is used as an input to the integral segments of the power control loop 42 and the automatic synchronization control loop 43, at which time the integral part of the PI controller for the power control loop 42 and the automatic synchronization control loop 43 will be disabled. When the energy storage converter 22 works in the off-grid mode, the energy storage converter 22 outputs the voltage which is the same as the load voltage before the temporary drop through the voltage control loop 42, and the mains supply is cut off from the power grid 1 by matching with the gate control signal of the thyristor 26, so that the off-grid work of the energy storage converter 22 is completed.
Similarly, if the energy storage converter 22 is in auto-synchronous mode, the S value will be defined as S =3, the PI controller integral part for the auto-synchronous control loop 43 will be immediately enabled, while 0 is used as an input to the power control loop 42 and voltage control loop 44 integral segments, at which time the integral part of the PI controller of the power control loop 42 and voltage control loop 44 will fail. The presynchronization control unit on the voltage control loop 44 synchronizes the voltage of the energy storage converter with the voltage of the power grid, triggers the thyristor 26 to conduct, and controls the current of the energy storage converter 22 to be reduced to the current during grid connection in a slow step manner, thereby completing the synchronous work of the energy storage converter 22 and the line of the power grid 1.
Step 2.2, in the coordinate transformation and power calculation unit 41, the converter outputs three-phase terminal voltage u pabc Three-phase mains voltage u gabc And the three-phase output current i of the converter pabc Respectively obtaining a component u under a dq coordinate system after abc/dq coordinate transformation pd ，u pq And u and gd ，u gq and i pd ，i pd And then obtaining the values of instantaneous active power P and instantaneous reactive power Q through an instantaneous active power and reactive power calculation link, wherein the calculation formula is as follows:
the rotation angle θ for coordinate transformation is expressed as follows:
θ＝∫(ω 0 +Δω+Δω syn )dt
in the formula, ω 0 Is a rated angular frequency value, delta omega is an output value of an active control part of the power control loop, and delta omega is a power control loop syn The output value is controlled for the q-axis component of the automatic contemporaneous control loop.
Step 2.3, the power control loop 42 consists of active and reactive control, as shown in fig. 3. The active power control loop obtains the instantaneous active power P after passing through a Low Pass Filter (LPF) LPF Then the active power is assigned a value P ref And P LPF And comparing, and outputting a delta omega value by the difference value through a PI controller. The reactive power control loop obtains the Q after passing the instantaneous reactive power Q through a Low Pass Filter (LPF) LPF Then, the reactive power is assigned to a value Q ref And Q LPF And comparing, and outputting the delta E value by the difference value through a PI controller.
And 2.4, the automatic synchronous control loop is formed by synchronous control of active components and reactive components of the voltage. The active component synchronous control loop transmits the active component u of the network voltage gd And the converter outputs an instantaneous active voltage value u pd Comparing, and outputting the difference value delta E through a PI controller syn The value is obtained. Reactive component synchronization control loop enables power grid voltage to have reactive component u gq And the converter outputs an instantaneous reactive voltage value u pq Comparing, and outputting the difference value to delta omega via PI controller syn The value is obtained.
And 2.5, the voltage control loop consists of an active component voltage control loop and a reactive component voltage control loop. Command value of active component voltage control loop
And the command value of the reactive component voltage control loop->
Calculated by the following equation:
wherein，E 0 For voltage feedforward values,. DELTA.E is the reactive power control loop output value,. DELTA.E syn And controlling an output value for the reactive component of the automatic synchronous control loop.
The voltage active component instruction value
And a feedback value u pd Comparing, outputting U by PI controller dref The value is obtained. Combining the voltage reactive component instruction value>
And a feedback value u pq Comparing, outputting U by PI controller qref The value is obtained. The U is dref And U qref After the dq/alpha beta coordinate transformation, the space vector pulse width modulation unit (SVPWM) 46 outputs the required PWM pulse to the switching tubes (S1-S6) in the energy storage converter 42, and the switching and exit of each working mode are realized by controlling the on-off of the switching tubes (S1-S6) through the PWM pulse.
The control strategy needs to continuously detect the condition of the power grid voltage and quickly and accurately judge whether voltage sag occurs according to the change of the power grid voltage. According to the continuous detection of the grid voltage and the converter output voltage component u under the dq coordinate system gd (active component of the grid voltage), u gq (reactive component of the grid voltage) and u pd (converter output instantaneous active voltage value), u pq (the converter outputs an instantaneous reactive voltage value), and whether the instantaneous reactive voltage value is greater than or equal to 0.9 times of a nominal voltage value (pu) of the power grid is judged, as shown in the following formula:
if the formula is met, the value of S is defined as S =1, which indicates that no voltage sag occurs, and at this time, the sensitive load is provided by the mains supply through the conducting thyristor, and the energy storage converter is in the grid-connected mode. If the voltage value is not satisfied, the voltage sag is generated at the moment, the gate signals of the thyristors are quickly turned off, the sensitive load is quickly switched to be supplied with power by the energy storage converter from the mains supply, the energy storage converter operates in an off-grid mode, and the value S is defined as S =2. Once the grid voltage is restored to the normal range from the sag, judging whether the following formula is met:
wherein U is thd And U thq Is the dq component control threshold that is automatically successful contemporaneously. If the formula is met, the automatic synchronization control is successful, the thyristor is immediately triggered to be conducted, the S value is defined as S =1, and the system is flexibly switched from being powered by the energy storage converter to being powered by mains supply.
The smooth switching and flexible exit method of the voltage sag device based on the voltage type control strategy can realize smooth switching and flexible exit with commercial power in the sag control process of the energy storage converter, and avoid current impact and power fluctuation caused by hard switching of a control mode due to no slowly-changing and current-changing link of the conventional energy storage converter. According to the method, a control framework is unified on the basis of no need of a current inner ring, the control complexity is reduced, the current inner ring is omitted on the basis of a voltage type control strategy, in addition, the voltage type converter is adopted, the control is more flexible, the response speed is higher, the sag can be managed in a shorter time, and experimental results show that (as shown in fig. 6 (a) and fig. 6 (b)), the energy storage converter can complete smooth switching within 3ms when the sag occurs.
The method comprises the following steps of judging the working mode of the energy storage converter according to the voltage condition output by a mains supply and the output voltage condition of the energy storage converter, and specifically comprises the following steps:
(1) And the energy storage converter judges the working mode according to the output voltage and the power grid voltage and enables the corresponding control module to work.
The first step is as follows: continuously detecting and calculating d-axis component u of power grid voltage gd Q-axis component u of the grid voltage gq And d-axis component u of output voltage of energy storage converter pd Q-axis component u of output voltage of energy storage converter pq ；
Second oneThe method comprises the following steps: judgment of
If the voltage is greater than or equal to 0.9 times of the nominal voltage value of the power grid, if the judgment result is yes, the voltage sag does not occur, the voltage sag may be just finished at the moment, then the third step is executed, otherwise, the voltage sag occurs, and the fourth step is executed;
the third step: according to u gd ，u gq And u pd ，u pq Judging whether the value is in a normal range, if so, possibly indicating that no sag occurs, or possibly just realizing automatic synchronization control, and then executing the fifth step, otherwise, executing the sixth step;
the fourth step: setting S =2, enabling a voltage control loop to work, enabling an energy storage converter to output voltage with the same amplitude frequency as the mains supply, closing a gate control signal of a thyristor and forcibly turning off the thyristor, quickly switching sensitive loads from mains supply to power supply provided by the energy storage converter, and enabling the energy storage converter to operate in an off-grid mode;
the fifth step: setting S =1, enabling a power control loop and a voltage control loop to work, reducing the output current of the energy storage converter by controlling the reference values of active power and reactive power of the power control loop, starting a gate control signal of a thyristor, enabling the converter to execute flexible exit control, switching the system from the flexible power supply of the energy storage converter to the flexible power supply of commercial power, and enabling the energy storage converter to be in a grid-connected mode;
and a sixth step: setting S =3, and executing automatic synchronization control.
The implementation steps are shown in the flow chart of fig. 4.
(2) Flexible exit control for energy storage converter
In order to implement the voltage sag control device flexible exit control method based on the voltage control strategy, as shown in fig. 5, the design program implementation steps are as follows:
the first step is as follows: determining that the energy storage converter is in an off-grid operation state at present, and setting S =2;
the second step: sampling three-phase alternating-current voltage output by a power grid; judging whether the energy storage converter needs to execute a grid-connected switching action or not at present;
the third step: if the parallel off-network switching action does not need to be executed, returning to the first step;
the fourth step: if the parallel network switching action needs to be executed, further judging whether the synchronous operation needs to be executed or not;
the fifth step: setting S =3 if the synchronous operation needs to be executed; otherwise, returning to the first step;
and a sixth step: reallocating the power control loop, the voltage control loop and the automatic synchronization control parameters according to the current value of S: if the current S =3, the power control loop integral is reset to zero, and the voltage control loop integral is enabled at the same time, and the synchronous control is enabled;
the seventh step: if the synchronous control is finished, triggering the thyristor to be conducted, and controlling the output current of the energy storage converter to be slowly reduced to zero from the current value at a certain rate;
eighth step: and judging whether the output current of the energy storage converter reaches the current in the grid-connected state, if the output current of the energy storage converter reaches the current in the grid-connected state, setting S =1, switching to the grid-connected state, and otherwise, continuously reducing the output current of the energy storage converter.
The embodiment of the invention also provides a smooth switching and flexible exiting device of the voltage sag treatment device, which comprises a working mode judging unit, a voltage control loop, a power control loop and an automatic synchronization control loop;
the working mode judging unit is used for judging the working mode of the energy storage converter according to the output voltage of the energy storage converter and the voltage of a power grid, and the working mode comprises a grid-connected mode, an off-grid mode and an automatic synchronization control mode;
the voltage control loop is used for enabling the energy storage converter to output voltage which is the same as the load voltage before voltage sag when the voltage sag is judged to occur, the power control loop and the voltage control loop enable the energy storage converter to output current to replace power grid current, and then commercial power is cut off from the power grid to finish smooth switching of commercial power supply to the energy storage converter;
and the voltage control loop and the automatic synchronization control loop are used for synchronizing the voltage of the energy storage converter and the voltage of the power grid when the voltage sag disappears, then the mains supply is connected into a load from the power grid, the current of the energy storage converter is controlled to be reduced to the current during grid connection in a slow step mode, the conversion between the energy storage converter and the power grid line is completed, and in the process, when the energy storage converter outputs active power and reactive power for a certain time respectively less than a threshold value, the energy storage converter is flexibly withdrawn and is completely supplied with power by the mains supply.
The integral link of the PI controller used for the power control loop, the automatic synchronization control loop and the voltage control loop is enabled or disabled by an S value, and the S value indicates different working modes of the energy storage converter.
The device also comprises a coordinate transformation and power calculation unit for calculating the three-phase terminal voltage u output by the energy storage converter pabc Three-phase network voltage u gabc And three-phase output current i pabc Respectively obtaining the output instantaneous active voltage value u of the energy storage converter under the dq coordinate system after abc/dq coordinate transformation pd The energy storage converter outputs an instantaneous reactive voltage value u pq And the active component u of the network voltage gd Reactive component u of the network voltage gq And three-phase output current active component i pd Three-phase output current reactive component i pd Then, instantaneous active and reactive power calculation is carried out to obtain the values of instantaneous active P and instantaneous reactive Q, and the calculation formula is as follows:
wherein the rotation angle θ for coordinate transformation is represented as follows:
θ＝∫(ω 0 +Δω+Δω syn )dt
in the formula, ω 0 Is a rated angular frequency value, delta omega is an output value of an active control part of the power control loop, and delta omega syn The output value is controlled for the q-axis component of the automatic contemporaneous control loop.
The power control loop comprises an active power control loop and a reactive power control loop,
the active power control loop is used for obtaining the instantaneous active power P after passing through a Low Pass Filter (LPF)To P LPF Then the active power is assigned a value P ref And P LPF Comparing, outputting delta omega value as output value of active control part of power control loop through PI controller,
the reactive power control loop is used for obtaining the instantaneous reactive power Q after passing through a Low Pass Filter (LPF) LPF Then, the reactive power is assigned to a value Q ref And Q LPF And comparing, and outputting the delta E value as the output value of the reactive part controlled by the power control loop through the PI controller.
The automatic synchronous control loop comprises an active component synchronous control loop and a reactive component synchronous control loop,
the active component synchronous control loop is used for controlling the active component u of the power grid voltage gd And the energy storage converter outputs an instantaneous active voltage value u pd Comparing, and outputting the difference value delta E through a PI controller syn The value is used as the output value of the active component control of the automatic synchronous control loop,
the reactive component synchronous control loop is used for converting the reactive component u of the power grid voltage gq And the energy storage converter outputs an instantaneous reactive voltage value u pq Comparing, and outputting the difference value delta omega through a PI controller syn And the value is used as the reactive component control output value of the automatic synchronous control loop.
The voltage control loop comprises an active component voltage control loop and a reactive component voltage control loop,
command value of the active component voltage control loop
And the command value of the reactive component voltage control loop->
Calculated by the following formula:
wherein E is 0 For voltage feed-forward values, Δ E is reactive powerRate control loop output value, Δ E syn Controlling an output value for an active component of an automatic synchronization control loop;
active component voltage control loop for providing a voltage active component command value
And a feedback value u pd Comparing, outputting U by PI controller dref A value;
the reactive component voltage control loop is used for converting the voltage reactive component instruction value
And a feedback value u pq Comparing, outputting U by PI controller qref Value of said U dref And U qref After the conversion processing of the dq/alpha beta coordinate conversion unit 45, the space vector pulse width modulation unit outputs the needed PWM pulse to a switch tube in the energy storage converter, and the switching and exit of each working mode are realized by controlling the on-off of the switch tube through the PWM pulse.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (9)
1. A smooth switching and flexible exit method of a voltage sag control device is characterized in that: the method comprises the following steps:
judging the working mode of the energy storage converter according to the output voltage of the energy storage converter and the voltage of a power grid, wherein the working mode comprises a grid-connected mode, an off-grid mode and an automatic synchronization mode;
when voltage sag occurs, the energy storage converter is switched from a grid-connected mode to an off-grid mode: enabling the energy storage converter to output voltage which is the same as the load voltage before the temporary drop through a voltage control loop, enabling the energy storage converter to output current to replace the current of a power grid through a power control loop and a voltage control loop, and then cutting off the commercial power from the power grid to finish the smooth switching of the commercial power supply to the energy storage converter;
when the voltage sag disappears, the energy storage converter is switched from an off-grid mode to a grid-connected mode: the voltage control loop and the automatic synchronization control loop are used for synchronizing the voltage of the energy storage converter with the voltage of a power grid, then mains supply is connected into a load from the power grid, the current of the energy storage converter is controlled in a slow step mode to be reduced to the current during grid connection, conversion between the energy storage converter and a power grid line is completed, and in the process, when active power and reactive power output by the energy storage converter are respectively smaller than threshold values, the energy storage converter is flexibly withdrawn and is completely powered by the mains supply.
2. The smooth switching and flexible exiting method of voltage sag management device according to claim 1, wherein: further comprising the steps of: the method comprises the steps of constructing a topological circuit, wherein the topological circuit comprises an energy storage body, an energy storage converter, a first isolating switch, a second isolating switch and a thyristor, a power grid is connected with a sensitive load through the first isolating switch, the thyristor and the second isolating switch, the output end of the energy storage body is connected between the thyristor and the second isolating switch after the energy storage body and the energy storage converter are connected in series, when the voltage of the power grid is normal, the energy storage converter is in an off-grid state, the sensitive load is powered by the power grid, and the output current of the energy storage converter is 0.
3. The smooth switching and flexible exiting method of voltage sag management device according to claim 1, wherein:
the specific steps of flexibly withdrawing the energy storage converter and completely supplying power by the mains supply are as follows: firstly, when the output voltage of the energy storage converter is adjusted to be in the same amplitude, the same frequency and the same phase with the mains supply by matching the automatic synchronous control loop with the voltage control loop, the selection state of the controller is modified to be S =1 at the moment, the integral enabling of the power controller is effective, the voltage controller keeps the integral ineffective, and then the active power instruction value P in the power control loop is gradually changed ref And do not haveWork power command value Q ref At this time, the active power command value P ref And an active power command value Q ref Gradually reducing to zero from the current value according to a certain speed, and when detecting that the active power and the reactive power output by the energy storage converter are respectively smaller than a threshold value P thd And Q thq As shown in the following formula:
at the moment, the PWM pulse output of the inter-vector pulse width modulation unit is closed, and the energy storage converter realizes flexible exit.
4. The utility model provides a voltage sag administers device smooth switch and flexible exit device which characterized in that includes mode of operation judgement unit, voltage control ring, power control ring, automatic synchronization control ring:
the working mode judging unit is used for judging the working mode of the energy storage converter according to the output voltage of the energy storage converter and the voltage of a power grid, and the working mode comprises a grid-connected mode, an off-grid mode and an automatic synchronization control mode;
the voltage control loop is used for enabling the energy storage converter to output voltage which is the same as the load voltage before voltage sag when the voltage sag is judged to occur, the power control loop and the voltage control loop enable the energy storage converter to output current to replace power grid current, and then commercial power is cut off from the power grid to finish smooth switching of commercial power supply to the energy storage converter;
and the voltage control loop and the automatic synchronization control loop are used for synchronizing the voltage of the energy storage converter and the voltage of the power grid when the voltage sag disappears, then the mains supply is connected into a load from the power grid, the current of the energy storage converter is slowly controlled to be reduced to the current during grid connection, the conversion between the energy storage converter and the power grid line is completed, and in the process, when the active power and the reactive power output by the energy storage converter are respectively smaller than the threshold value, the energy storage converter is flexibly withdrawn and is completely supplied with power by the mains supply.
5. The voltage sag management device smooth switching and flexible exiting device of claim 4, wherein: and the integral links of the PI controllers for the power control loop, the automatic synchronization control loop and the voltage control loop are enabled or disabled by an S value, and the S value represents different working modes of the energy storage converter.
6. The voltage sag management device smooth switching and flexible exiting device of claim 4, wherein: the device also comprises a coordinate transformation and power calculation unit which is used for calculating the three-phase terminal voltage u output by the energy storage converter pabc Three-phase network voltage u gabc And three-phase output current i pabc Respectively obtaining the instantaneous active voltage value u output by the energy storage converter under the dq coordinate system after abc/dq coordinate transformation pd Energy storage converter outputs instantaneous reactive voltage value u pq And the network voltage active component u gd Reactive component u of the grid voltage gq And three-phase output current active component i pd Three-phase output current reactive component i pd Then, instantaneous active and reactive power calculation is carried out to obtain the values of instantaneous active P and instantaneous reactive Q, and the calculation formula is as follows:
wherein the rotation angle θ for coordinate transformation is represented as follows:
θ＝∫(ω 0 +Δω+Δω syn )dt
in the formula, ω 0 Is a rated angular frequency value, delta omega is an output value of an active control part of the power control loop, and delta omega syn The output value is controlled for the q-axis component of the automatic contemporaneous control loop.
7. The device for smooth switching and flexible exit of a voltage sag management device according to claim 6, wherein: the power control loop comprises an active power control loop and a reactive power control loop,
the active power control loop is used for reducing the instantaneous active power PP is obtained after passing through a filter (LPF) LPF Then the active power is assigned a value P ref And P LPF Comparing, outputting delta omega value as output value of active control part of power control loop through PI controller,
the reactive power control loop is used for obtaining the instantaneous reactive power Q after passing through a Low Pass Filter (LPF) LPF Then, the reactive power is assigned to a value Q ref And Q LPF And comparing, and outputting the delta E value as the output value of the reactive part controlled by the power control loop through the PI controller.
8. The voltage sag management device smooth switching and flexible exiting device of claim 7, wherein: the automatic synchronous control loop comprises an active component synchronous control loop and a reactive component synchronous control loop,
the active component synchronous control loop is used for controlling the active component u of the power grid voltage gd And the energy storage converter outputs an instantaneous active voltage value u pd Comparing, and outputting the difference value delta E through a PI controller syn The value is used as the output value of the active component control of the automatic synchronous control loop,
the reactive component synchronous control loop is used for controlling the reactive component u of the grid voltage gq And the energy storage converter outputs an instantaneous reactive voltage value u pq Comparing, and outputting the difference value to delta omega via PI controller syn And the value is used as the reactive component control output value of the automatic synchronous control loop.
9. The voltage sag management device according to claim 8, wherein said device for smooth switching and flexible exit is characterized in that: the voltage control loop comprises an active component voltage control loop and a reactive component voltage control loop,
command value of the active component voltage control loop
And the command value of the reactive component voltage control loop->
Calculated by the following formula:
wherein E is 0 Is the voltage feedforward value, delta E is the reactive power control loop output value, delta E syn Controlling an output value for an active component of an automatic synchronization control loop;
active component voltage control loop for providing voltage active component command value
And a feedback value u pd Comparing, outputting U by PI controller dref A value;
the reactive component voltage control loop is used for converting the voltage reactive component instruction value
And a feedback value u pq Comparing, outputting U by PI controller qref Value of said U dref And U qref After the conversion processing of the dq/alpha beta coordinate conversion unit, the space vector pulse width modulation unit outputs the needed PWM pulse to a switch tube in the energy storage converter, and the switching and exit of each working mode are realized by controlling the on-off of the switch tube through the PWM pulse. />
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| CN112383070A (en) * | 2020-11-19 | 2021-02-19 | 珠海格力电器股份有限公司 | Control method, device and system for off-grid and grid-connected switching of microgrid |
| CN112787344A (en) * | 2021-01-27 | 2021-05-11 | 广州智光储能科技有限公司 | Control method and device for switching parallel energy storage converters from off-grid to on-grid |
| CN113394791A (en) * | 2021-05-24 | 2021-09-14 | 苏州爱科赛博电源技术有限责任公司 | Parallel DVR bypass thyristor rapid cut-off control method |
| CN114374260A (en) * | 2021-11-03 | 2022-04-19 | 上海富硕信息科技有限公司 | Computer room power control system and control method |
| CN114744661B (en) * | 2022-06-10 | 2022-09-16 | 四川大学 | Industrial user side multifunctional electrochemical energy storage system and operation control method |
| CN114977200B (en) * | 2022-08-03 | 2022-09-30 | 东方博沃（北京）科技有限公司 | Quick turn-off method of thyristor, electronic equipment and storage medium |
| CN117239776A (en) * | 2023-08-25 | 2023-12-15 | 国网湖北省电力有限公司电力科学研究院 | Target area voltage sag control method, device, system and medium |
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