CN113395033B - Control method and system for low voltage ride through of high-voltage frequency converter - Google Patents
Control method and system for low voltage ride through of high-voltage frequency converter Download PDFInfo
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- CN113395033B CN113395033B CN202110764343.5A CN202110764343A CN113395033B CN 113395033 B CN113395033 B CN 113395033B CN 202110764343 A CN202110764343 A CN 202110764343A CN 113395033 B CN113395033 B CN 113395033B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
- H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
- H02P23/14—Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage
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Abstract
The invention discloses a control method and a system for low voltage ride through of a high voltage frequency converter, relating to the technical field of high voltage frequency conversion, wherein the incoming line low voltage condition of a high voltage frequency converter system is divided into three areas of transient state, dynamic state and steady state, a low voltage ride through control strategy is designed aiming at each area, the low voltage output capability of the high voltage frequency converter is maximized, and a control strategy of 'rated magnetic flux control maximum current limit automatic deceleration operation' is firstly provided aiming at a dynamic crossing region, the strategy can realize that when the voltage of the incoming line power supply of the high-voltage frequency converter drops to not less than 60 percent of rated voltage, continuously outputs with the maximum power allowable by the frequency converter, ensures the long-term safe operation of the power supply object, realizes the simplicity, the system disturbance is small, and the control of low-voltage ride through of the high-voltage frequency converter with long-time small amplitude voltage drop can be adapted.
Description
Technical Field
The invention relates to the technical field of high-voltage frequency conversion, in particular to a control method and a control system for low-voltage ride through of a high-voltage frequency converter.
Background
The high-power water pump and the fan are widely applied to the industrial fields of energy, steel making, cement, coal ore mining and the like, and because of the requirements of the process, energy conservation and the like, a high-voltage frequency converter is mostly adopted for speed regulation driving at present. When the frequency converter drives the motor, if the voltage of a power supply inlet line is reduced in a transient state, a dynamic state or a long time due to external faults or disturbance of power supply object equipment in a power grid, the frequency converter does not take any measures, and the following problems can be caused: 1. when the voltage of the incoming line is reduced, the current of the frequency converter is increased, and if the power allowance of the frequency converter is insufficient, the overcurrent trip fault of the frequency converter can be generated. 2. Most of the high-voltage frequency converter units control power to the unit bus voltage, and if the voltage drop amplitude is too large, unit power failure can be caused, and the frequency converter is stopped. The stable operation of the high-power water pump and the fan is very important for the aspects of production safety, process quality, yield and the like in various industrial fields, so that the industrial driving application occasions all require that the high-voltage frequency converter needs to have low-voltage ride through capability for coping with the drop of a power grid.
At present, the low voltage ride through of a high voltage frequency converter mostly adopts a rotating speed tracking restarting control mode after short-time power failure. Under the control mode, when the power supply voltage is reduced and exceeds a certain range, the frequency converter stops outputting but does not trip, at the moment, the motor is in a free braking state, the rotating speed is gradually reduced, if the power supply voltage is recovered to be normal in a specified waiting time, the frequency converter restarts in a mode of tracking rotating speed restarting, wherein the mode of tracking rotating speed restarting estimates the electromechanical frequency of the motor according to the counter electromotive force of the motor, when the high-voltage frequency converter recovers, the frequency converter starts to work from the estimated electric frequency, so that the restarting process is stable and has no impact), the instantaneous fluctuation of the power supply voltage can be avoided, and if the power supply voltage is not recovered to be normal in the waiting time, the frequency converter considers that the power supply low-voltage fault occurs and trips to stop the vehicle.
When the fault type is transient, the bus voltage is generally rapidly reduced and rapidly recovered; when the fault occurs for a long time, the low voltage of the bus needs to be kept for a long time, so that the restarting time of the frequency converter can avoid the voltage fluctuation time of a long time, and the function of the frequency converter can be exerted to the maximum extent. The low-voltage ride through scheme which independently adopts a 'rotating speed tracking restart control mode after short power failure' is more effective in the situation that the voltage drop duration time does not exceed 5s, but along with the increase of the voltage drop time, the reliability of the method can be greatly reduced, but the requirement for a long-time low-voltage ride through function of the high-voltage frequency converter is urgent in the current industrial application environment.
Disclosure of Invention
In view of this, the present invention provides a method and a system for controlling low voltage ride through of a high voltage inverter, which are simple, have less disturbance to the system, and are suitable for low voltage ride through control of a high voltage inverter with a long-time small amplitude voltage droop.
In a first aspect, an embodiment of the present invention provides a control method for low voltage ride through of a high voltage inverter, which is applied to an input/output system of the high voltage inverter, and specifically comprises a power supply, the high voltage inverter and a motor, and the method includes the steps of:
s1: dividing a low-voltage ride through zone of a frequency converter power supply into a transient state interval, a dynamic interval and a steady state interval according to the voltage drop condition; the voltage drop condition comprises a voltage drop amplitude and a voltage drop speed;
s2: when the voltage drop condition falls into a transient interval, the high-voltage frequency converter performs low-voltage ride through by adopting a mode of tracking the rotating speed and restarting;
s3: when the voltage drop condition falls into a dynamic range, the high-voltage frequency converter adopts a mode of maximum current limit depth flux weakening control of rated magnetic flux to carry out low-voltage ride through;
s4: when the voltage drop condition falls into a steady-state interval, the stable operation is maintained and the low voltage ride through is carried out through the capacity allowance of the high-voltage frequency converter.
In the embodiment, in view of the fact that the voltage of the transient, dynamic or long-time power supply inlet line caused by external faults or disturbances of the high-voltage frequency converter and the power supply object equipment is reduced to the specified high-low voltage crossing area, when the voltage drop amplitude does not exceed a certain degree, the high-voltage frequency converter can stably drive the motor to operate for a long time according to the maximum output capacity of the high-voltage frequency converter by reasonably processing different transient, dynamic and steady states, namely the long-time low-voltage crossing capacity is formed, the reliability of the low-voltage crossing technology is enhanced, power can be reliably supplied, and the safe operation of the power supply object is guaranteed.
In one possible embodiment, in the low voltage ride through, a master control system in the high voltage frequency converter sets a low voltage ride through control algorithm, and the master control system acquires input side voltage data, output side voltage data and output side current data of the high voltage frequency converter; the input side voltage and the output side voltage are measured by arranging a voltage transformer in the input and output system of the high-voltage frequency converter, and the output side current data are measured by arranging a current transformer in the input and output system of the high-voltage frequency converter; and the low voltage ride through control algorithm adjusts the amplitude and the frequency of the modulation signal according to the data of the voltage at the input side, the voltage at the output side and the current at the output side of the high-voltage frequency converter.
In one possible embodiment, in step S2, the method includes:
detecting the time length that the incoming line voltage of the input and output system of the high-voltage frequency converter falls into a transient interval;
when the time length of the transient interval exceeds 1ms, the high-voltage frequency converter stops outputting but does not trip, the back electromotive force of the motor is sampled through the output side voltage transformer, and the rotating speed of the motor is calculated according to the back electromotive force;
judging whether the incoming line voltage of the high-voltage frequency converter is recovered to be normal or not according to the incoming line voltage amplitude, and calculating the frequency and amplitude of the output voltage of the frequency converter according to the rotating speed calculated by the back emf so as to ensure that the rotating speed of the motor is stable and can be recovered to be normal without impact; if the time length of the incoming line voltage amplitude value falling into the transient area exceeds a certain time length (usually 2s, the parameter can be set according to specific engineering), the situation that the incoming line voltage of the high-voltage frequency converter is abnormal is judged, the high-voltage frequency converter is failed to restart, and a heavy fault is reported to shut down. In one possible embodiment, in step S3, the method includes:
detecting the time length of the incoming line voltage of the input and output system of the high-voltage frequency converter falling into a dynamic interval;
when the time length falling into the dynamic interval exceeds 1ms, judging the voltage modulation degree of the high-voltage frequency converter; and when the voltage modulation degree is not full, outputting a voltage modulation signal amplitude increment delta Amp by taking rated magnetic flux control as a target, and when the voltage modulation degree is full, the input and output system of the high-voltage frequency converter can not maintain rated magnetic flux operation.
In one possible embodiment, when the input and output system of the high-voltage frequency converter can not maintain the rated magnetic flux operation any more, if the incoming line voltage continues to decrease, the output current of the high-voltage frequency converter gradually increases; the high-voltage frequency converter outputs operation frequency increment delta Freq in a range not exceeding rated current, and when the delta Freq is a negative value, the output load of the high-voltage frequency converter is reduced; and when the voltage of the high-voltage frequency converter is recovered to be normal, adjusting the amplitude increment delta Amp and the operating frequency increment delta Freq of the output voltage modulation signal to be 0.
Preferably, the transient interval is that the amplitude after voltage sag is greater than or equal to 20% Un and less than 60% Un, and the voltage sag speed is greater than or equal to 264 kV/s.
Preferably, the dynamic interval is that the amplitude is greater than or equal to 60% Un and less than or equal to 90% Un after voltage drop and the voltage drop speed is less than or equal to 264 kV/s.
Preferably, the steady-state interval is that the amplitude is greater than 90% Un after voltage drop and the voltage drop speed is less than or equal to 264 kV/s.
In a second aspect, an embodiment of the present invention provides a control system for low voltage ride through of a high voltage inverter, where the high voltage inverter is connected to a three-phase alternating current of a power supply and controls output of the three-phase alternating current to a motor, and the high voltage inverter includes:
the current transformer is used for measuring and outputting the current data;
the voltage transformer is used for measuring voltage data of input and output sides;
the master control system is connected with the current transformer and the voltage transformer, is internally provided with a low-voltage ride through control algorithm, is used for adjusting the amplitude and the frequency of modulation data according to output measurement data and input and output side voltage data, and sends the amplitude and the frequency to the PWM module;
and the PWM modulation module is used for generating a switching pulse signal according to the amplitude and the frequency of the modulation data and controlling the on-off of each power switching device of the high-voltage frequency converter.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. according to the control method and the system for low-voltage ride through of the high-voltage frequency converter, when the voltage of a transient, dynamic or long-time power supply inlet line caused by external faults or disturbance of the high-voltage frequency converter and power supply object equipment is reduced to a specified high-voltage and low-voltage ride through area, power can be reliably supplied, the safe operation of a power supply object is guaranteed, when the voltage drop amplitude does not exceed a certain degree, the high-voltage frequency converter can stably drive a motor to operate for a long time according to the maximum output capacity of the high-voltage frequency converter, namely the long-time low-voltage ride through capacity is formed, and the reliability of a low-voltage ride through technology is enhanced;
2. the control method and the system for low voltage ride through of the high-voltage frequency converter provided by the embodiment of the invention realize reliable power supply and guarantee the safe operation of a power supply object when the voltage of an incoming line power supply of the high-voltage frequency converter falls to a region with the duration time not exceeding 5s and the voltage of the incoming line power supply falling to be not less than 20% of rated voltage; when the voltage of an incoming line power supply drops to not less than 60% of rated voltage, the high-voltage frequency converter can continuously output with the maximum allowable power of the frequency converter, so that the long-term safe operation of a power supply object is ensured; when the voltage of the incoming line power supply of the high-voltage frequency converter drops to not less than 90% of rated voltage, the frequency converter can reliably supply power, and the safe operation of a power supply object is guaranteed.
Drawings
In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and that for those skilled in the art, other related drawings can be obtained from these drawings without inventive effort.
Fig. 1 is a schematic flow chart of a control method for low voltage ride through of a high voltage inverter according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a control system for low voltage ride through of a high voltage inverter according to an embodiment of the present invention;
fig. 3 is a control block diagram of low voltage ride through of the high voltage inverter according to the embodiment of the present invention;
fig. 4 is a control block diagram of the high-voltage inverter falling into the dynamic range according to the embodiment of the present invention;
fig. 5 is a diagram of processing low voltage ride through (lv-ht) actual data of a high voltage inverter according to an embodiment of the present invention;
FIG. 6 is a data diagram of per unit value of motor current amplitude provided by an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those of ordinary skill in the art that: it is not necessary to employ these specific details in order to practice the present invention. In other instances, well-known structures, circuits, materials, or methods have not been described in detail so as not to obscure the present invention.
Throughout the specification, reference to "one embodiment," "an embodiment," "one example" or "an example" means: the particular features, structures, or characteristics described in connection with the embodiment or examples are included in at least one embodiment of the invention. Thus, the appearances of the phrases "one embodiment," "an embodiment," "one example" or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combination and/or sub-combination in one or more embodiments or examples. Further, those of ordinary skill in the art will appreciate that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In the description of the present invention, the terms "front", "rear", "left", "right", "upper", "lower", "vertical", "horizontal", "upper", "lower", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and therefore, should not be construed as limiting the scope of the present invention.
Examples
The inventor researches and discovers that the low-voltage ride-through scheme is effective under the condition that the voltage drop duration time is not more than 5s at present, but the reliability of the method is greatly reduced along with the increase of the voltage drop duration time, so that the method has urgent requirements on the long-time low-voltage ride-through function of the high-voltage frequency converter in the current industrial application environment, how to realize the method is simple, and the problem of reducing system disturbance to realize the long-time low-voltage ride-through control of the high-voltage frequency converter in the small-amplitude voltage drop is solved.
Referring to fig. 2, fig. 2 is a control system for low voltage ride through of a high voltage frequency converter according to an embodiment of the present invention, which includes a power supply, the high voltage frequency converter and a motor, where the high voltage frequency converter specifically includes a current transformer, a voltage transformer, a main control system and a PWM modulation module. The high-voltage high-power frequency converter is characterized in that a low-voltage ride-through control algorithm is implanted into the main control system of the high-voltage high-power frequency converter through a low-voltage ride-through high-voltage high-power frequency converter, and the control algorithm needs to obtain information of input and output side voltages and output currents of the frequency converter. The system respectively measures input side voltage information and output side voltage information through the PT device, measures output current information through the CT device, and then adjusts the amplitude and frequency of a modulation signal according to the information through a low-voltage ride-through control algorithm in the main control system, so that the on-off of each power switch device is controlled, the incoming line voltage state is adapted, and the motor and a load system thereof can be guaranteed to ride through a low-voltage area with minimum power fluctuation.
Referring to fig. 1, fig. 1 is a control method for low voltage ride through of a high voltage frequency converter according to an embodiment of the present invention, in practical application, a low voltage ride through region of a power supply of the frequency converter is divided according to a voltage drop amplitude and a voltage drop speed to form three low voltage ride through regions of a transient state, a dynamic state and a steady state, and when a voltage drop condition meets a transient low voltage ride through region condition, the high voltage frequency converter performs low voltage ride through in a "rotational speed tracking and restarting control mode after short power off"; when the voltage drop condition accords with the dynamic low-voltage crossing region condition, the high-voltage frequency converter adopts 'maximum current limit value depth weak magnetic automatic speed reduction operation control under rated magnetic flux control'; when the voltage drop condition meets the steady-state crossing region condition, the high-voltage frequency converter does not take any measures, and stably runs by using the capacity allowance of the frequency converter to cross the low-voltage region.
As a preferred embodiment of the foregoing embodiment, in performing low voltage ride through, a master control system in the high voltage frequency converter sets a low voltage ride through control algorithm, and the master control system acquires data of input-side voltage, output-side voltage, and output-side current of the high voltage frequency converter; the input side voltage and the output side voltage are measured by arranging a voltage transformer in the input and output system of the high-voltage frequency converter, and the output side current data are measured by arranging a current transformer in the input and output system of the high-voltage frequency converter; and the low voltage ride through control algorithm adjusts the amplitude and the frequency of the modulation signal according to the data of the voltage at the input side, the voltage at the output side and the current at the output side of the high-voltage frequency converter.
In practical application, in order to cope with the complex incoming line low-voltage condition, the low-voltage crossing region is divided according to the amplitude after voltage drop and the voltage drop speed. The frequency converter is divided into transient state crossing areas when the voltage of an incoming line power supply falls within a range of 20-60% of rated voltage or the voltage change speed is higher than 264kV/s, and the high-voltage frequency converter needs to be ensured to complete crossing under the condition that the duration time of a low-voltage state is less than 5s in the area; dividing the high-voltage frequency converter into dynamic crossing regions when the voltage falls within a range of 60-90% of rated voltage and the voltage change speed is less than 264kV/s, and ensuring that the high-voltage frequency converter can run for a long time in a load reduction state to cross a low-voltage region in the region; when the voltage falls in the range above 90% of rated voltage and the voltage change speed is less than 264kV/s, the high-voltage frequency converter is divided into steady-state crossing areas, and the high-voltage frequency converter can stably run for a long time to cross a low-voltage area in the area, which is specifically detailed in table 1.
TABLE 1
Referring to fig. 1 and fig. 3, in order to implement the operation requirement of the crossing region, a corresponding low voltage crossing control scheme needs to be formulated according to different crossing regions. When the condition that the low voltage of the inlet wire of the system belongs to the transient state crossing region and exceeds 1ms is detected, the frequency converter enters a control strategy of 'tracking and restarting the rotating speed after short-time power failure', a frequency converter stops outputting but does not trip, then samples the counter potential of the motor in real time through outputting PT, estimates the rotating speed of the motor according to the counter potential value, tracks the rotating speed of the motor to be stable and have no impact and restart after the inlet wire voltage of the frequency converter returns to be normal within the set 'waiting time', and reports a fault and stops if the frequency converter is failed to restart.
As shown in fig. 4, when it is detected that the low voltage of the incoming line of the system belongs to a dynamic crossing area exceeding 1ms, the frequency converter enters a control strategy of 'rated magnetic flux control maximum current limit automatic speed reduction operation', if the voltage modulation degree of the frequency converter is not full under the control strategy, the rated magnetic flux control is taken as a target, amplitude increment Δ Amp of a voltage modulation signal is output, if the voltage modulation degree is full, the system cannot maintain rated magnetic flux operation any more, at this time, if the voltage of the incoming line is continuously reduced, the output current of the frequency converter is gradually increased, the frequency converter is to ensure that the amplitude of the output current is not more than 1.0 time of the rated current as the target output operation frequency increment Δ Freq, and if the Δ Freq is a negative value, the system is to automatically reduce the speed to reduce the output load of the frequency converter, thereby ensuring that the system does not have the situation of overcurrent trip. When the incoming line voltage of the frequency converter automatically recovers to a normal condition, the amplitude increment delta Amp and the operating frequency increment delta Freq of the output voltage modulation signal are adjusted to be 0, and at the moment, the system can stably and undisturbed quit the control of 'rated magnetic flux control maximum current limit automatic deceleration operation' and recover to a normal operating state.
In addition, when the system inlet wire low voltage is detected to belong to the steady-state crossing region, the high-voltage frequency converter can keep the normal state for long-time operation by utilizing the capacity margin of the high-voltage frequency converter.
As shown in fig. 5 and 6, the invention is specifically applied to a high-voltage frequency converter of a circulating water pump of a rear stone power plant, and is used for solving the problem that the incoming line voltage is gradually reduced when the power frequency of an electric feed water pump is started. As shown in fig. 5 and 6, after the power frequency of the electric feed water pump is started, the service voltage is gradually reduced by about 70% of the rated voltage, and as the voltage of the voltage inlet line is reduced, the output current of the high-voltage frequency converter of the circulating water pump is gradually increased, and finally, an output overcurrent trip occurs. After the application of the invention, the maximum value of the output current of the frequency converter is only 1.17 times of the rated current (the instantaneous overcurrent is 1.5 times of the rated current), thereby ensuring that the high-voltage frequency converter passes through similar long-time low-voltage conditions.
In summary, the main problem to be solved by the present invention is that firstly, the incoming line low voltage condition of the high voltage inverter system is divided into three areas of transient state, dynamic state and steady state, and a low voltage ride through control strategy is designed for each area in a targeted manner, so as to maximize the low voltage output capability of the high voltage inverter. And moreover, a control strategy of 'rated magnetic flux control maximum current limit automatic speed reduction operation' is provided for the first time aiming at a dynamic crossing region, and the strategy can realize that the high-voltage frequency converter continuously outputs at the maximum power allowable by the frequency converter under the condition that the voltage of an inlet wire power supply drops to not less than 60% of rated voltage, so that the long-term safe operation of a power supply object is ensured.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A control method for low voltage ride through of a high voltage frequency converter is provided, wherein an input and output system of the high voltage frequency converter consists of a power supply, the high voltage frequency converter and a motor, and the method is characterized by comprising the following steps:
dividing a low-voltage ride through zone of a frequency converter power supply into a transient state interval, a dynamic interval and a steady state interval according to the voltage drop condition; the voltage drop condition comprises a voltage drop amplitude and a voltage drop speed;
when the voltage drop condition falls into a transient interval, the high-voltage frequency converter performs low-voltage ride through in a mode of tracking the rotating speed and restarting;
when the voltage drop condition falls into a dynamic interval, the high-voltage frequency converter adopts a mode of maximum current limit depth flux weakening control of rated flux to carry out low-voltage ride through;
when the voltage drop condition falls into a steady-state interval, the stable operation is maintained and the low voltage ride through is carried out through the capacity allowance of the high-voltage frequency converter;
when the voltage drop condition falls into a dynamic interval, the high-voltage frequency converter adopts the maximum current limit value depth flux weakening control mode of rated flux to carry out low-voltage ride through, and the method comprises the following steps:
detecting the time length of the incoming line voltage of the input and output system of the high-voltage frequency converter falling into a dynamic interval;
when the time length of falling into the dynamic interval exceeds 1ms, judging the voltage modulation degree of the high-voltage frequency converter; when the voltage modulation degree is not full, outputting a voltage modulation signal amplitude increment delta Amp by taking rated magnetic flux control as a target, and when the voltage modulation degree is full, the input and output system of the high-voltage frequency converter can not maintain rated magnetic flux operation any more;
when the maximum current limit depth flux weakening control of rated magnetic flux is performed when the input and output system of the high-voltage frequency converter can not maintain the rated magnetic flux operation any more, if the voltage of the incoming line is continuously reduced, the output current of the high-voltage frequency converter is gradually increased; the high-voltage frequency converter outputs operation frequency increment delta Freq with the amplitude not exceeding the rated current, and when the delta Freq is a negative value, the output load of the high-voltage frequency converter is reduced; and when the voltage of the high-voltage frequency converter is recovered to be normal, adjusting the amplitude increment delta Amp and the operating frequency increment delta Freq of the output voltage modulation signal to be 0.
2. The control method for low voltage ride through of a high voltage inverter according to claim 1, wherein in performing low voltage ride through, a master control system in the high voltage inverter sets a low voltage ride through control algorithm, and the master control system acquires input-side voltage, output-side voltage and output-side current data of the high voltage inverter; the input side voltage and the output side voltage are measured by arranging a voltage transformer in the input and output system of the high-voltage frequency converter, and the output side current data are measured by arranging a current transformer in the input and output system of the high-voltage frequency converter; and the low voltage ride through control algorithm adjusts the amplitude and the frequency of a modulation signal according to the data of the voltage at the input side, the voltage at the output side and the current at the output side of the high-voltage frequency converter.
3. The method for controlling the low voltage ride through of the high voltage inverter according to claim 2, wherein when the voltage drop condition falls into the transient section, the high voltage inverter performs the low voltage ride through by restarting according to the tracking rotation speed, comprising:
detecting the time length of the incoming line voltage of the input and output system of the high-voltage frequency converter falling into a transient interval;
when the time length of the transient interval exceeds 1ms, the high-voltage frequency converter stops outputting but does not trip, the back electromotive force of the motor is sampled through the output side voltage transformer, and the rotating speed of the motor is calculated according to the back electromotive force;
judging whether the voltage of the incoming line of the high-voltage frequency converter is recovered to be normal or not according to the amplitude of the voltage at the input side, and calculating the frequency and the amplitude of the output voltage of the frequency converter according to the motor rotating speed calculated by the back electromotive force to ensure that the motor rotating speed is stable and can be recovered to be normal without impact; if the time length that the incoming line voltage amplitude value falls into the transient area exceeds a certain time length, the incoming line voltage of the high-voltage frequency converter is judged to be abnormal, the high-voltage frequency converter is restarted to fail, and a heavy fault is reported to shut down.
4. The method as claimed in claim 1, wherein the transient interval is 20% Un or more and 60% Un or less after voltage sag, and the voltage sag speed is 264kV/s or more.
5. The method as claimed in claim 1, wherein the dynamic range is that after a voltage drop, the amplitude is greater than or equal to 60% Un and less than or equal to 90% Un, and the voltage drop speed is less than or equal to 264 kV/s.
6. The method as claimed in claim 1, wherein the steady state interval is a voltage sag amplitude greater than 90% Un and a voltage sag speed less than or equal to 264 kV/s.
7. A control system for low voltage ride through of a high voltage frequency converter comprises a power supply, the high voltage frequency converter and a motor, and is characterized in that the control system is used for realizing the control method according to any one of claims 1 to 6, the high voltage frequency converter is connected with three-phase alternating current of the power supply to control and output to the motor, and comprises:
the current transformer is used for measuring and outputting the current data;
the voltage transformer is used for measuring voltage data of input and output sides;
the master control system is connected with the current transformer and the voltage transformer, is internally provided with a low-voltage ride-through control algorithm, is used for adjusting the amplitude and the frequency of modulation data according to output measurement data and input and output side voltage data, and sends the amplitude and the frequency to the PWM module;
and the PWM modulation module is used for generating a switching pulse signal according to the amplitude and the frequency of the modulation data and controlling the on-off of each power switching device of the high-voltage frequency converter.
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