阅读说明：本技术 一种异步变频电机减速过压抑制方法 (Deceleration overvoltage suppression method for asynchronous variable frequency motor ) 是由 沈开雄 喻杰 徐前 于 2019-09-05 设计创作，主要内容包括：本发明提供了一种异步变频电机减速过压抑制方法,在不增加外部装置的前提下,针对至少接入一台变频器的工况,采用闭环PID控制,快速、平稳地抑制异步变频电机的母线电压波动,输出电流、转矩平稳。本发明为电压单闭环控制,减少了计算量,最终达到与现有双闭环控制方法一致的母线电压抑制效果。本发明为全减速过程PID调节,解决了电机减速初始阶段母线电压冲击的问题。本发明加入了减速时间补偿功能,保证整个减速过程耗时等于或最接近于用户设定的减速时间,使减速时间最优。(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.)

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 U_dc；

S3: setting the overvoltage suppression point voltage as U^* _dcCalculating the voltage U of the overvoltage suppression point^* _dcWith the current bus voltage U_dcVoltage deviation Δ U of (1):

ΔU＝U^* _dc-U_dc；

s4: adjusting the proportional parameter K of the PID regulator according to the voltage deviation Delta U_pIntegral parameter K_iDifferential parameter K_d；

S5: calculating the actual frequency decrement Δ f by means of a PID regulator_Real；

S6: will be the actual frequencyThe incremental amount of the rate Δ f_RealSending 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 f_runTarget operating frequency of f_refThe total deceleration time is the deceleration time set by the user as T_decThe used deceleration time is T_usedSampling time of T_sampleThen, the ideal frequency decrement Δ f is:

Δf＝(f_run-f_ref)/(T_dec-T_used)/T_sample。

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 K_pAnd a differential parameter K_dPlays a main regulating role; once Δ U < 0 occurs, and regardless of the subsequent variation, the scaling parameter K_pAnd an integral parameter K_iPlays 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 DeltaU_nLast cycle voltage deviation of Δ U_n-1The voltage deviation DeltaU passes through the output P of the PID regulator_outComprises the following steps:

wherein P is_outHas a value range of [0, 4096%]Then the actual frequency is decreased by an amount Δ f_RealComprises the following steps:

Δf_Real＝(4096-P_out)·Δf/4096。

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 U_dc；

S3: setting the overvoltage suppression point voltage as U^* _dcCalculating the voltage U of the overvoltage suppression point^* _dcWith the current bus voltage U_dcVoltage deviation Δ U of (1):

ΔU＝U^* _dc-U_dc；

s4: adjusting the proportional parameter K of the PID regulator according to the voltage deviation Delta U_pIntegral parameter K_iDifferential parameter K_d；

S5: calculating the actual frequency decrement Δ f by means of a PID regulator_Real；

S6: decrement the actual frequency by Δ f_RealSending 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 f_runTarget operating frequency of f_refThe total deceleration time is the deceleration time set by the user as T_decThe used deceleration time is T_usedSampling time of T_sampleThen, the ideal frequency decrement Δ f is:

Δf＝(f_run-f_ref)/(T_dec-T_used)/T_sample。

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 K_pAnd a differential parameter K_dPlays a main regulating role; once Δ U < 0 occurs, and regardless of the subsequent variation, the scaling parameter K_pAnd an integral parameter K_iPlays 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 DeltaU_nLast cycle voltage deviation of Δ U_n-1The voltage deviation DeltaU passes through the output P of the PID regulator_outComprises the following steps:

wherein P is_outHas a value range of [0, 4096%]Then the actual frequency is decreased by an amount Δ f_RealComprises the following steps:

Δf_Real＝(4096-P_out)·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 f_runTarget operating frequency of f_refThe total deceleration time is the deceleration time set by the user as T_decThe used deceleration time is T_usedSampling time of T_sampleThen, the ideal frequency decrement Δ f is:

Δf＝(f_run-f_ref)/(T_dec-T_used)/T_sample。

s2: sampling the current bus voltage value U_dc。

S3: setting the overvoltage suppression point voltage as U^* _dcCalculating the voltage U of the overvoltage suppression point^* _dcWith the current bus voltage U_dcVoltage deviation Δ U of (1):

ΔU＝U^* _dc-U_dc。

s4: adjusting the proportional parameter K of the PID regulator according to the voltage deviation Delta U_pIntegral parameter K_iDifferential parameter K_d: in the initial stage of deceleration, when delta U is more than or equal to 0, the proportional parameter K_pAnd a differential parameter K_dPlays a main regulating role; once Δ U < 0 occurs, and regardless of the subsequent variation, the scaling parameter K_pAnd an integral parameter K_iPlays 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 regulator_Real: let the current period voltage deviation be DeltaU_nLast cycle voltage deviation of Δ U_n-1The voltage deviation DeltaU passes through the output P of the PID regulator_outComprises the following steps:

wherein P is_outHas a value range of [0, 4096%]Then the actual frequency is decreased by an amount Δ f_RealComprises the following steps:

Δf_Real＝(4096-P_out)·Δf/4096。

s6: decrement the actual frequency by Δ f_RealAnd 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 U_max(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 output_Reall is as close as possible to the ideal frequency decrement af. If Δ f ═ Δ f_RealAnd 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.