CN112448630A - Deceleration overvoltage suppression method for asynchronous variable frequency motor - Google Patents
Deceleration overvoltage suppression method for asynchronous variable frequency motor Download PDFInfo
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- CN112448630A CN112448630A CN201910836810.3A CN201910836810A CN112448630A CN 112448630 A CN112448630 A CN 112448630A CN 201910836810 A CN201910836810 A CN 201910836810A CN 112448630 A CN112448630 A CN 112448630A
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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
- H02P23/0004—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control
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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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- 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
- H02P23/20—Controlling the acceleration or deceleration
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Abstract
The invention provides a method for restraining reduction overvoltage of an asynchronous variable frequency motor, which adopts closed-loop PID control to quickly and stably restrain the bus voltage fluctuation of the asynchronous variable frequency motor and stabilize the output current and the torque aiming at the working condition of at least one frequency converter on the premise of not increasing an external device. The invention is voltage single closed-loop control, reduces the calculated amount and finally achieves the bus voltage suppression effect consistent with the existing double closed-loop control method. The invention is PID adjustment in the full deceleration process, and solves the problem of bus voltage impact in the initial deceleration stage of the motor. The invention adds the deceleration time compensation function, ensures that the time consumed in the whole deceleration process is equal to or closest to the deceleration time set by a user, and ensures that the deceleration time is optimal.
Description
Technical Field
The invention belongs to the technical field of motor deceleration overvoltage suppression, and particularly relates to a deceleration overvoltage suppression method for an asynchronous variable frequency motor.
Background
When the asynchronous variable frequency motor dragging system decelerates, the rotating speed (synchronous rotating speed) of the rotating magnetic field of the motor immediately drops, but the rotating speed of the rotor cannot drop immediately due to the mechanical inertia of the dragging system; then the rotor speed is higher than the synchronous speed, the direction of the rotor winding cutting the magnetic field is opposite to the former direction, and the motor is in a power generation state. The torque shear on the motor shaft is braking torque, so that the rotating speed of the motor is promoted to be rapidly reduced, and the state is called a regenerative braking state; in the whole deceleration process, mechanical energy on a motor shaft is converted into regenerative braking electric energy to be input into the frequency converter, a part of the regenerative braking electric energy is consumed in a loop of the motor and the frequency converter, and the rest is accumulated on a bus capacitor, so that the bus voltage is increased.
In the existing asynchronous variable frequency motor dragging system, the bus voltage is limited within a safe range by controlling regenerative braking electric energy; the common solutions are four:
1. the plurality of frequency converters share a direct current bus, so that the motor which runs electrically absorbs the regenerative electric energy of the speed reducing motor;
2. a feedback device is additionally arranged to feed the regenerative braking electric energy back to the power grid;
3. a brake unit is additionally arranged, and regenerative braking electric energy is eliminated through the energy consumption of a brake resistor;
4. the speed reduction time of the frequency converter is prolonged, and the regenerative braking electric energy consumed by the motor and the frequency converter is fully utilized. The 'overvoltage suppression point voltage' and 'deceleration time' are preset in the parameters of the frequency converter, and the deceleration time (frequency decrement) is adjusted in real time according to the change of the bus voltage, so that the regenerative braking electric energy generated in unit time can be completely consumed on the frequency converter and the motor. The method specifically comprises two modes:
firstly, a bus voltage hysteresis control method: stopping decelerating when the voltage of the bus is higher than the voltage of the overvoltage suppression point, and keeping the motor running at the current frequency; and continuing to reduce the frequency and speed after the bus voltage returns to normal.
A voltage-active power double closed-loop control method: calculating target active power through PI regulation according to the bus voltage and the voltage value of the inhibition point; and according to the target active power and the sampling active power of the frequency converter, obtaining the frequency decrement of the synchronous rotating speed through PI regulation, and reducing the frequency.
In the solution for suppressing the speed reduction and overvoltage of the asynchronous variable frequency motor, the method 1 is suitable for the working condition that a plurality of frequency converter buses are used in parallel, and is ineffective for the working condition of a single frequency converter; in the methods 2 and 3, an external device needs to be additionally arranged, and the external device has failure risk, so that the system cost and the later maintenance difficulty are increased; the method 4 solves the overvoltage problem by automatically adjusting the frequency converter, is most convenient to apply, but has the following problems in specific effect:
the voltage hysteresis control method is characterized in that the rotating speed of the motor is cyclically reciprocated between a speed reduction state and a holding state and a speed reduction state during speed reduction, so that the voltage of a bus is repeatedly fluctuated, the output current is fluctuated along with the fluctuation of the voltage of the bus, and the torque fluctuation and the rotating speed instability of the motor are caused; on the other hand, the bus voltage repeatedly charges and discharges the electrolytic capacitor, which affects the service life of the capacitor.
The 'voltage-active power' double closed-loop control method is divided into two adjusting loops of voltage and active power, and the whole control system is complex; the accuracy of the control key variable 'instantaneous active power' is influenced by the output voltage, the output current detection accuracy and the program calculation.
In both modes, the bus voltage is regulated after being higher than the overvoltage suppression point voltage, the bus voltage is not controlled in the early stage of deceleration, and an impulse voltage larger than the overvoltage suppression point voltage is easily generated. In order to ensure that the bus voltage in the whole process is in a safe range, the set value of the overvoltage suppression point voltage can only be reduced, the consumption capability of regenerative braking electric energy is weakened, and the deceleration time is prolonged; on the other hand, the impact of voltage also has certain influence on the service life of the bus capacitor.
Both of these approaches do not optimize the deceleration time. The optimal deceleration time is the whole deceleration process, and the actual deceleration time is equal to or closest to the deceleration time of the frequency converter set by the user. After the bus voltage is higher than the overvoltage suppression point voltage in the deceleration process, the frequency converter automatically prolongs the deceleration time; the subsequent regenerative braking energy is reduced, and the deceleration process cannot be accelerated to compensate for the early-stage prolonged deceleration time after the bus voltage is lower than the overvoltage suppression point voltage.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method is used for quickly and stably inhibiting the bus voltage fluctuation of the asynchronous variable frequency motor aiming at the working condition of at least one frequency converter under the premise of not increasing an external device.
The technical scheme adopted by the invention for solving the technical problems is as follows: a speed reduction overvoltage suppression method for an asynchronous variable frequency motor comprises the following steps:
s1: after receiving a deceleration command, a frequency converter of the asynchronous motor enters a deceleration overvoltage suppression mode, and an ideal frequency increment amount delta f in the residual deceleration process is calculated according to parameters including the current operating frequency, the target operating frequency, the deceleration time set by a user and the time used for deceleration;
s2: sampling the current bus voltage value Udc；
S3: setting the overvoltage suppression point voltage as U* dcCalculating the voltage U of the overvoltage suppression point* dcWith the current bus voltage UdcVoltage deviation Δ U of (1):
ΔU＝U* dc-Udc；
s4: adjusting the proportional parameter K of the PID regulator according to the voltage deviation Delta UpIntegral parameter KiDifferential parameter Kd；
S5: calculating the actual frequency decrement Δ f by means of a PID regulatorReal；
S6: decrement the actual frequency by Δ fRealSending the frequency to a frequency control unit of the frequency converter to output the frequency of the synchronous rotating speed;
s7: judging whether the deceleration process is finished or not, and if so, stopping the deceleration process; if not, the step S1 is executed circularly until the deceleration process is finished.
According to the scheme, in the step S1, the specific steps are as follows:
let the current operating frequency be frunTarget operating frequency of frefThe total deceleration time is the deceleration time set by the user as TdecThe used deceleration time is TusedSampling time of TsampleThen, the ideal frequency decrement Δ f is:
Δf＝(frun-fref)/(Tdec-Tused)/Tsample。
further, in step S4, the specific steps include: in the initial stage of deceleration, when delta U is more than or equal to 0, the proportional parameter KpAnd a differential parameter KdPlays a main regulating role; once Δ U < 0 occurs, and regardless of the subsequent variation, the scaling parameter KpAnd an integral parameter KiPlays a main regulating role; the larger the parameter is, the stronger the regulating effect is; the smaller the parameter, the weaker the regulating action.
Further, in step S5, the specific steps include:
let the current period voltage deviation be DeltaUnLast cycle voltage deviation of Δ Un-1The voltage deviation DeltaU passes through the output P of the PID regulatoroutComprises the following steps:
wherein P isoutHas a value range of [0, 4096%]Then the actual frequency is decreased by an amount Δ fRealComprises the following steps:
ΔfReal＝(4096-Pout)·Δf/4096。
the invention has the beneficial effects that:
1. the method for restraining the speed reduction and overvoltage of the asynchronous variable frequency motor quickly and stably restrains the bus voltage fluctuation of the asynchronous variable frequency motor aiming at the working condition of at least one frequency converter under the premise of not increasing an external device.
2. The invention adopts closed-loop PID control to maintain the bus voltage within the range of 'overvoltage suppression point voltage' +/-2V, and output current and torque are stable.
3. The method is voltage single closed-loop control, simplifies a control system, reduces the calculated amount, avoids the influence of inaccurate active power calculation and current sampling on the regulation effect, and finally achieves the bus voltage suppression effect consistent with the conventional double closed-loop control method.
4. The invention adopts the PID adjustment of the full deceleration process, solves the problem of bus voltage impact at the initial stage of motor deceleration by adopting the PID parameter of the self-adaptive regulator, is beneficial to improving the set value of overvoltage suppression point voltage and quickens the deceleration process.
5. The invention adds the deceleration time compensation function, ensures that the bus voltage is lower than the overvoltage suppression point voltage, automatically accelerates the deceleration process to compensate the earlier-stage prolonged deceleration time, ensures that the time consumption of the whole deceleration process is equal to or closest to the deceleration time set by a user, and ensures that the deceleration time is optimal; if the synchronous rotating speed is decreased by the ideal frequency decreasing amount in the deceleration process, the final actual deceleration time is consistent with the deceleration time set by the user.
Drawings
FIG. 1 is a flow chart of an embodiment of the present invention.
Fig. 2 is a graph of bus voltage versus time comparing an embodiment of the present invention to a conventional method.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Referring to fig. 1, the method for suppressing the speed reduction and overvoltage of the asynchronous variable frequency motor comprises the following steps:
s1: after receiving a deceleration command, a frequency converter of the asynchronous motor enters a deceleration overvoltage suppression mode, and the current operating frequency is set to be frunTarget operating frequency of frefThe total deceleration time is the deceleration time set by the user as TdecThe used deceleration time is TusedSampling time of TsampleThen, the ideal frequency decrement Δ f is:
Δf＝(frun-fref)/(Tdec-Tused)/Tsample。
s2: sampling the current bus voltage value Udc。
S3: setting the overvoltage suppression point voltage as U* dcCalculating the voltage U of the overvoltage suppression point* dcWith the current bus voltage UdcVoltage deviation Δ U of (1):
ΔU＝U* dc-Udc。
s4: adjusting the proportional parameter K of the PID regulator according to the voltage deviation Delta UpIntegral parameter KiDifferential parameter Kd: in the initial stage of deceleration, when delta U is more than or equal to 0, the proportional parameter KpAnd a differential parameter KdPlays a main regulating role; once Δ U < 0 occurs, and regardless of the subsequent variation, the scaling parameter KpAnd an integral parameter KiPlays a main regulating role; the larger the parameter is, the stronger the regulating effect is; the smaller the parameter, the weaker the regulating action.
S5: calculating the actual frequency decrement Δ f by means of a PID regulatorReal: let the current period voltage deviation be DeltaUnLast cycle voltage deviation of Δ Un-1The voltage deviation DeltaU passes through the output P of the PID regulatoroutComprises the following steps:
wherein P isoutHas a value range of [0, 4096%]Then the actual frequency is decreased by an amount Δ fRealComprises the following steps:
ΔfReal＝(4096-Pout)·Δf/4096。
s6: decrement the actual frequency by Δ fRealAnd sending the frequency to a frequency control unit of the frequency converter to output the frequency of the synchronous rotating speed.
S7: judging whether the deceleration process is finished or not, and if so, stopping the deceleration process; if not, the step S1 is executed circularly until the deceleration process is finished.
Referring to fig. 2, in the conventional method, when the bus voltage is greater than the overvoltage suppression point voltage U for the first time* dcNamely, the adjustment is started at the time t2, the system is in an open-loop uncontrollable state in the previous deceleration process, namely, the time t 1-t 2, and the bus voltage can impact Umax(ii) a The invention starts to adjust from the moment t1, adopts the PID adjusting method of full deceleration process parameter self-adaptation, effectively restrains the impulse voltage, and ensures that the maximum voltage of the bus is at the overvoltage restraining point voltage U* dcNearby. The invention reduces the risk of overvoltage alarm of the frequency converter and improvesOvervoltage suppression point voltage U* dcThe consumption of the regenerative braking electric energy of the motor is accelerated, and the deceleration time of the system is shortened.
The method calculates the ideal frequency increment delta f in real time, and ensures that the bus voltage is maintained at the overvoltage suppression point voltage U* dcOn a nearby basis, the actual frequency decrement Δ f of the control outputReall is as close as possible to the ideal frequency decrement af. If Δ f ═ Δ fRealAnd l, the actual deceleration time of the motor is consistent with the deceleration time set by the user.
The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes and modifications made in accordance with the principles and concepts disclosed herein are intended to be included within the scope of the present invention.
Claims (4)
1. A method for suppressing deceleration overvoltage of an asynchronous variable frequency motor is characterized by comprising the following steps: the method comprises the following steps:
s1: after receiving a deceleration command, a frequency converter of the asynchronous motor enters a deceleration overvoltage suppression mode, and an ideal frequency increment amount delta f in the residual deceleration process is calculated according to parameters including the current operating frequency, the target operating frequency, the deceleration time set by a user and the time used for deceleration;
s2: sampling the current bus voltage value Udc；
S3: setting the overvoltage suppression point voltage as U* dcCalculating the voltage U of the overvoltage suppression point* dcWith the current bus voltage UdcVoltage deviation Δ U of (1):
ΔU＝U* dc-Udc；
s4: adjusting the proportional parameter K of the PID regulator according to the voltage deviation Delta UpIntegral parameter KiDifferential parameter Kd；
S5: calculating the actual frequency decrement Δ f by means of a PID regulatorReal；
S6: will be the actual frequencyThe incremental amount of the rate Δ fRealSending the frequency to a frequency control unit of the frequency converter to output the frequency of the synchronous rotating speed;
s7: judging whether the deceleration process is finished or not, and if so, stopping the deceleration process; if not, the step S1 is executed circularly until the deceleration process is finished.
2. The method for suppressing the deceleration overvoltage of the asynchronous variable frequency motor according to claim 1, characterized in that: in the step S1, the specific steps are as follows:
let the current operating frequency be frunTarget operating frequency of frefThe total deceleration time is the deceleration time set by the user as TdecThe used deceleration time is TusedSampling time of TsampleThen, the ideal frequency decrement Δ f is:
Δf＝(frun-fref)/(Tdec-Tused)/Tsample。
3. the method for suppressing the deceleration overvoltage of the asynchronous variable frequency motor according to claim 2, characterized in that: in the step S4, the specific steps are as follows: in the initial stage of deceleration, when delta U is more than or equal to 0, the proportional parameter KpAnd a differential parameter KdPlays a main regulating role; once Δ U < 0 occurs, and regardless of the subsequent variation, the scaling parameter KpAnd an integral parameter KiPlays a main regulating role; the larger the parameter is, the stronger the regulating effect is; the smaller the parameter, the weaker the regulating action.
4. The method for suppressing the deceleration overvoltage of the asynchronous variable frequency motor according to claim 3, characterized in that: in the step S5, the specific steps are as follows:
let the current period voltage deviation be DeltaUnLast cycle voltage deviation of Δ Un-1The voltage deviation DeltaU passes through the output P of the PID regulatoroutComprises the following steps:
wherein P isoutHas a value range of [0, 4096%]Then the actual frequency is decreased by an amount Δ fRealComprises the following steps:
ΔfReal＝(4096-Pout)·Δf/4096。
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113411033A (en) * | 2021-07-15 | 2021-09-17 | 中冶赛迪工程技术股份有限公司 | Method for judging input overvoltage of load with motor of frequency converter |
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