RU2461951C1 - Adaptation method of current limitation set point for formation of start-up and braking trajectories of asynchronous motors of pump units - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in adaptation method of current limitation set point there measured is instantaneous and actual supply voltage values and current values in stator windings of asynchronous motor and at the intervals determined by conditions of the water supply process, condition of electrical network and time required for performance of computer calculations of characteristics of current energy conversion process in electrical network - smooth start device - asynchronous motor with short-circuited rotor - pump - pipeline system; maximum possible current limitation set point is calculated for smooth start device, at the development of which throughout the controlled start of asynchronous motor there met are the limitations specified in technical requirements, and change the actual current limitation set point value.

EFFECT: reduction of electric power loses in windings of asynchronous motor with short-circuited rotor, which operates in electrical network - smooth start device - asynchronous motor with short-circuited rotor - pump - pipeline system by adaptation of current limitation set point at controlled formation of start-up and braking trajectories.

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Description

The invention relates to electrical engineering and can be used in various industries, agriculture and housing and communal services. The technical result consists in reducing energy losses in the windings of a squirrel-cage induction motor operating in the system “electric network - soft starter (soft starter) - squirrel-cage induction motor (AM) - pump - pipeline".

The known method [1], which is characterized by the following set of features similar to the set of essential features of the invention: three-phase voltage is supplied through three pairs of counter-parallel connected thyristors to the stator windings of an induction motor, and control signals from a pulse-phase control system are fed to the control inputs of the thyristors . In this case, the signal corresponding to the opening angle of the thyristors is fed to the input of the pulse-phase control system in such a way as to ensure the constancy of the predetermined current value in the stator windings for the period of starting the induction motor.

The disadvantages of the method are: a) the difficulty of setting parameters (gain and integration constant) of the current regulator in a device that implements this method taking into account the required dynamic characteristics of the electric drive; b) does not realize the possibility of reducing the loss of electrical energy in the windings of an induction motor in transient conditions.

Closest to the invention is a method [2], which is characterized by the following set of features: a three-phase voltage is supplied through three pairs of counter-parallel connected thyristors to the stator windings of an induction motor, and control signals from a synchronized current-phase pulse-phase control system are fed to the control inputs of the thyristors stator winding, at the input of which a signal is supplied in the form of a voltage equivalent to the opening angle of the thyristors, the value of which at each moment of time is set in advance , The measured current and the instantaneous value of the mains voltages and currents in the induction motor stator windings and their deviation from the set values stopping supplying control signals to the thyristors. This identification method is taken as a prototype.

The disadvantage of the prototype is that it does not realize the possibility of reducing the loss of electrical energy in the windings of an induction motor in transient conditions. In the structure of energy losses in the AM of the pumping station of the water supply system (Fig. 1), the most significant part belongs to losses in the stator and motor rotor windings [3, 4], while the power of losses in the stator and rotor windings of the three-phase AM is as follows:

.where R _s (R _r ) is the active resistance of the stator (rotor) winding HELL; i _sα (t), i _sβ (t), i _sγ (t) [i _rα (t), i _rβ (t), i _rγ (t)] - instantaneous stator (rotor) currents of blood pressure in α-β-γ coordinate system [3, 4]. Energy losses during the transition process (T _P ) are:

.

Figure 2 shows graphs of changes in energy losses in blood pressure during direct (uncontrolled) start-up ΔW _NP in relation to energy losses during a smooth (controlled) start ΔW _UP as a function of the duration of the rise of the control angle (t _ramp ) from α _min to α _max (angles the opening of the thyristors, providing the lower and upper levels of the operating voltage at the output of the SSC) during start-up, based on the typical shape of the control angle curve shown in Fig. 3. T _n in the calculation of the integral of said time taken, in which the instantaneous angular speed of the rotor BP ω _r (t) and fell further not leave range _{ω r (t) ∈ [0.95} · ω r, y; 1.05 · ω _{r, y} ], where ω _{r, y} is the steady-state value of the angular velocity of the AB rotor.

Figure 2 shows the minimum energy loss caused by a decrease in the oscillation of state variables during the transition process. At t _{ramp, opt} = 0.02 ... 0.03 s, the loss ΔW _{UP is} reduced by 14-20% compared with the energy loss during uncontrolled start ΔW _NP . A further increase in t _ramp leads to an increase in losses due to an increase in the time spent by the blood pressure in the region of reduced speed. The increase in losses occurs faster with a decrease in the nominal power of blood pressure and an increase in the mechanical load on the motor shaft. Thus, an unreasonable increase in the duration of a soft start results in an excess of energy losses compared with direct start. Figure 4 shows the dependences of the coefficient of multiplicity of the stator current during a controlled start for the above BP with a similar change in the load on the shaft. The dependence of the current multiplicity coefficient for a controlled start-up k _{I, UP} = I _up / I _n = f (T _P ), where I _UP , A is the inrush current of the AM, I _n is the rated current of the stator windings of the AM, monotonously decreases with increasing t _ramp .

When using the AB start-up algorithm with current limitation, the user sets the value of the maximum allowable ratio k _{I, UE} , which determines the total duration of start-up T _P. In this case, when using the same value of k _{I, UE} for all AM of pumping units, the changes are not taken into account in the system “electric network - UPP - HELL - pump - pipeline", introduced by starting the next engine, and also does not take into account the influence of interfaced systems on the voltage of the electric network. In particular, the choice of an underestimated value of k _{I, UE} leads to an unreasonable delay in starting, which cannot be considered optimal from the point of view of energy saving; the choice of an overestimated value of k _{I, UE} cannot guarantee a safe operating mode for the windings of the AM and the pipeline. Thus, in order to reduce the loss of electrical energy in the windings of induction motors of the pumping station of the water supply system, it is necessary to develop an algorithm for calculating k _{I, UP} , which ensures the convergence of T _P to its, using the mathematical model of the system “electric network - UPP - AD - pump - pipeline” the optimal value (T _{n, opt)} corresponding t _{ramp, opt,} subject to satisfaction of constraints imposed on parameters transients with subsequent correction of the current setpoint value Stall cheniya.

1. The magnitude of the shock inrush current AD I _UP (the largest amplitude of the stator currents of the motor during the transient process) should not cause a drop in the nominal voltage at the point of general connection to the network below the value ΔU _{max, additional} , established by GOST 13109-97. The fulfillment of this condition ensures the normal operation of the electrical equipment of the pumping station, including computer technology, instrumentation and others.

2. The value of I _UP should not exceed the amplitude of the starting current HELL (I _P ), set by the manufacturer of this engine. Fulfillment of this condition will protect the windings of the motor windings from mechanical overloads that exceed the value set by the manufacturer.

3. The nature of the change in the currents of the stator windings HELL during the transition process should not cause an increase in the steady-state temperature of the stator windings HELL θ _s above the maximum permissible average value Θ _{max, additional} established by GOST 8865-93 for an insulation system of the corresponding heat resistance class.

4. The duration of the transition process (T _P ) should be selected based on two restrictions. On the one hand, the arising free component of the stator currents of blood pressure should not lead to a violation of conditions 1-3. On the other hand, the largest increase in pressure in the pipeline ΔP _max caused by the transient process should not exceed the maximum allowable value ΔP _{max, add} .

An object of the invention is to reduce the loss of electrical energy in the windings of induction motors of the pumping unit of the water supply system by adapting the current limit setting with the controlled formation of start-brake trajectories.

The essence of the claimed method of adapting the current limit setting for the formation of start-brake trajectories of asynchronous motors of pumping units is that the three-phase voltage is supplied through three pairs of counter-parallel connected thyristors to the stator windings of the asynchronous motor, and control signals from the system are sent to the thyristor control inputs phase control, current-synchronized stator windings of an induction motor, to the input of which a signal is supplied in the form of voltage, equivalent the opening angle of the thyristors, the value of which is set in advance at each moment in time, measure the instantaneous and effective values of the network voltage and current in the stator windings of the induction motor and, when they deviate from the set values, stop supplying control signals to the thyristors, and differs in that the instant and current values of network voltage and current in the stator windings of an induction motor and with a frequency determined by the conditions of the water supply process, the state of the electric of the power network and the time it takes to perform computer calculations of the characteristics of the current energy conversion process in the system "electric network - soft starter - squirrel-cage induction motor - pump - pipeline", the maximum possible current limit setting for the soft starter is calculated, during which it is continued during a controlled start asynchronous motor, the constraints specified by the technical requirements are satisfied and the current value of the current limit setting is changed Niya.

Figure 1 shows the functional diagram of the ACS by the soft start of the asynchronous motor of the pumping station of the water supply system, which illustrates the relationship within the system "electric network - soft starter - HELL - pump - pipeline".

Figure 2 shows the graphs of changes in energy losses in an induction motor with direct (uncontrolled) starting ΔW _NP in relation to energy losses with a smooth (controlled) starting ΔW _UP as a function of the duration of the rise of the control angle (t _ramp ) from α _min to α _max . The curves were plotted for two induction motors with a value of the moment of resistance on the shaft M _c1 = {0.1M _n1 , 0.5M _n1 , M _n1 } for the 4AS132S4U3 motor (rated power R _n = 8.5 kW) with a nominal electromagnetic moment M _n1 = 58 N · m and M _s2 = {0.1M _n2 , 0.5M _n2 , M _n2 } for a 4AS250M4U3 engine (P _n = 63 kW) with a nominal torque M _n2 = 430 N · m, respectively.

Figure 3 presents a typical curve shape of the control angle, where α _min corresponds to the opening angle of the thyristors, providing a lower level of the effective voltage at the output of the converter. α _max corresponds to the opening angle of the thyristors, which provides the upper level of the effective voltage at the output of the converter. α _kik and t _kik - the value of the angle and the duration of the starting (kick) pulse, designed to create the desired starting moment.

Figure 4 shows the dependences of the ratio of the stator current multiplicity k _{I, UP} = I _UP / I _n , where I _UP , A - shock inrush current HELL, I _n - nominal current of the stator windings HELL, A with a controlled start.

Figure 5 presents the logical diagram of the claimed algorithm for adapting the current limit setting, where I _UP , A - shock inrush current HELL, _IP , A - inrush current (according to the manufacturer), k _{I, UP} - current multiplicity factor for a controlled start, I _U , A - current setting when controlling the soft starter according to the current-limited algorithm, T _P , s - the duration of the transient process.

Figure 6 presents the mathematical model of the ACS by the soft start of the asynchronous motor of the pumping station of the water supply system, consisting of mathematical models (MM) of several subsystems.

Figure 7 shows the structure of the initial data of the algorithm, where the restrictions imposed on the course of the start-up and brake processes in the pump station BP, which can be divided into two groups: fixed, due to the type of used BP ( _IP , ах _{max , add} ), and varying depending on the operating conditions of the NS (ΔU _{max, add} , ΔР _{max, add} ).

On Fig presents a logical diagram of the predictor block of the algorithm, the result of the predictor are the values of the duration of the start T * _{P, i} and the starting current I * _{P, I} , with which the i-th blood pressure pump unit can be started while satisfying the restrictions on ΔU _{max, add} and ΔР _{max, add} .

Figure 9 presents the logical diagram of the block corrector algorithm, if not all the engines are running, then the return is carried out with the transfer of control to the predictor. At the end of the calculations, the calculated optimal values of the stator current multiplicity coefficient k _{opt, i} = I _{U, i} / I _{n, i} for each of the AMs are sequentially sent to the soft starter to work out the start according to the current-limited algorithm.

Figure 10 presents the comparative simulation results of the soft start of asynchronous motors of the pumping station using traditional and adaptive algorithms.

To implement the claimed method, a traditional BP start is used with the help of a soft starter according to a program with current limitation, at which the current setting I _U is set the same for all BP of the main pumps, i.e. I _Y = I _{Y, 1} = I _{Y, 2} = ... = I _{Y, n.} The start-brake trajectories of blood pressure are formed according to the algorithm proposed in [5, 6, 7], the essence of which is as follows.

1. Discrete time samples t _i , i = l, 2, 3 ... n are introduced, in which condition I _UP = k · I _U is met, where k is the safety factor.

2. At time t ₁ = 0, the control angle α takes the initial value α = α ₀ .

3. At the current time t _{i, the} angle α is calculated according to the following rule:

where k _f is the frequency of the sinusoidal control curve.

Before starting the first motor AD ₁ in the secondary circuit of the power transformer (Fig. 1), the effective line voltage has a value of U _{st, 1} , in the pipeline there is a steady head H _{st, 1} , which together with the initial flow rate Q _H determine the value of the resistance moment M _{s , 1 of the} first centrifugal pump. The controlled start of the first blood pressure begins at time t _{start, 1} when the appropriate command is sent to the soft starter. In continuation of the transition process: (1) the appearing starting currents cause a voltage drop in the electric network by ΔU ₁ ; (2) the temperature of the stator windings of blood pressure rises to Θ ₁ ; (3) the water pressure in the pipeline increases by an amount whose maximum value is ΔH ₁ . At the end of the transition process, a pressure H _{st, 2 is} established in the pipeline, which together with the flow rate Q _n will determine the value of the resistance moment M _{s, 2 of the} second centrifugal pump. In this order, all n HELLs of pumping units are started, and at the start of each subsequent engine, the initial conditions are the values of the model state variables obtained when starting the previous HELLs.

The results of the analysis of energy losses in blood pressure during a controlled start-up (Figs. 2, 4) allow us to conclude that the use of a fixed current setting for starting all the blood pressure of the pumping station cannot be considered effective. The choice of an underestimated value of I _Y leads to an unreasonable delay in starting and energy losses, as follows from the analysis of the graphs of FIG. 2; the choice of an overestimated value of I _U leads to voltage dips in the network below the maximum permissible value, and can also cause a water hammer in the pipeline. The logical scheme of the claimed algorithm for adapting the current limit settings of the pumping station of the water supply system, eliminating these disadvantages, is shown in Fig.5. The calculations in this algorithm are performed using mathematical models from [8, 9, 10, 11], combined into a model of an ACS system by soft start of an asynchronous motor of a pumping station (Fig.6).

To implement the claimed method, a database (DB) is preliminarily formed, into which the initial information is entered in the following categories (Fig. 7): electrical subsystem (parameters of the power transformer and AM, including the thermophysical parameters of the AD materials); mechanical subsystem (parameters of centrifugal pumps); hydraulic subsystem (parameters of the main pipeline, bypass line, tanks). Upon completion of the entry and verification of all the source data, the procedure for initializing the variables and parameters of the algorithm is carried out. Then control is transferred to the predictor (Fig. 8), which performs two procedures.

The first procedure involves obtaining j readings of the maximum pressure increase ΔP _{max, ij} in the pipeline as a function of the duration of the start of the i-th BP T i _{, ij} . Samples are calculated automatically by numerically integrating the hydraulic subsystem model, and their results are approximated. In particular, for this purpose, you can use the dependence ΔP _max = f (T _P ) in the form:

ΔP _max = a ₁ · exp (a ₂ · T _P ) + a ₃ · exp (a ₄ · T _P ),

where a _j , j = 1, 2 ... 4 are constant coefficients. The monotonic nature of this function allows us to state that for calculating constant coefficients the minimum required number of points {ΔP _{max, ij} ; T _{P, ij} } corresponds to the number of unknowns, that is, n = 4. If the samples of the function ΔP _{max, i} = f (T _{P, i} ) for the hydraulic subsystem of a given configuration have already been obtained, then the values of the constant coefficients of the function are read from the database of the program. As a result of the approximation, the value of T * _{P, i} corresponding to the established restriction ΔP _{max, add} .

The second predictor procedure is associated with the study of an electrical system, which includes: a source of infinite power sinusoidal current with a nominal voltage of the power line; step-down power transformer and already started HELL (if any), for which a simplified equivalent circuit is used, corresponding to the nominal operating mode. As a result of the study, the values of the amplitude of the maximum permissible current I _{UP, additional} , corresponding to the established limitation ΔU _{max, additional} , and inrush current I * _{UP, i} = min (I _{UP, additional} , I _{P, i} ), where I _{P, i} - starting current of the i-th blood pressure, corresponding to the catalog data of the manufacturer. Thus, the result of the predictor operation is the start duration T * _{P, i} and the inrush current I * _{UP, I} , with which the i-th blood pressure of the pump unit can be started while satisfying the restrictions on ΔU _{max, additional} and ΔP _{max, additional} .

, определяется оптимальная уставка тока

- фиг.2. В противном случае, т.е. при Т*_П,i>Т_П,опт, с использованием аппроксимирующей функции I_УП,i=f(T_П,i) определяется такое значение I_У,I, для которого выполняются два условия: I_У,i≤I*_УП,i при Т_П,i=f(I_У,i)≥Т*_П,i.Then control is transferred to the corrector (Fig.9), which also performs two procedures. The first procedure involves obtaining j samples of the starting current I _{UP, ij} depending on the duration of the start-up T _{P, ij} for the i-th blood pressure. Samples are calculated automatically by numerically integrating the SIFU-TPN-AD model. The form of the dependence I _UP = f (T _P ) is similar to the dependence ΔP _max = f (T _P ). If the sampling of the function I _{UP, i} = f (T _{P, i} ) for the i-th AD with the current moment of resistance on the shaft M _{c, i} has already been obtained, then the values of the constant coefficients are read from the database of the program. For a value of T * _{P, I} , less than or equal to

, the optimum current setting is determined

- figure 2. Otherwise, i.e. at T * _{P, i} > T _{P, opt} , using the approximating function I _{U , i} = f (T _{P, i} ), such a value I _{U, I} is determined for which two conditions are satisfied: I _{U, i} ≤I * _{UE , i} at Т _{П, i} = f (I _{У, i} ) ≥Т * _{П, i} .

The second corrector procedure is related to the fact that for the obtained values of I _{U, i} , T _{P, i} , the maximum temperature Θ _{max, i of the} frontal parts of the stator windings of the i-th blood pressure is calculated. If the condition Θ _{max, i} > Θ _{max, add} , is fulfilled, then a message is displayed about the inadmissible conditions for starting the current AM due to temperature overheating of the windings. In this case, it is necessary to consider the possibility of easing the varied restrictions ΔP _{max, additional} and ΔU _{max, additional} and recalculate the value of Θ _{max, i} . If not all engines are started, then a return is made with control transfer to the predictor. At the end of the calculations, the calculated optimal values of k _{opt, i} = I _{Y, i} / I _{n, i} for each of the AMs are sequentially sent to the soft starter to work out the start according to the current-limited algorithm.

Comparative simulation results of a smooth start of the pump station BP using the traditional and declared adaptive algorithms show (Fig. 10) that a smooth start of the pump circuit using the adaptive algorithm can reduce the total energy loss in the windings of the BP by approximately 18% in relation to the energy loss when using the classical algorithm with a fixed setpoint k _{I, UP} = 3. Moreover, a decrease in k _{I, UP} by 0.5 leads to an increase in losses by

. Увеличение k_I,УП до значения k_I,УП=5 приводит к превышению максимального прироста давления в трубопроводе выше установленного ограничения ΔP_mах,доп на половину. Кроме того, при значении k_I,УП=6 происходит падение напряжения в первичной и вторичной цепях трансформатора на величину ΔU_max=10,1%, что нарушает установленное ограничение ΔU_mах,доп=10%. Применение заявленного алгоритма адаптации уставки токоограничения для формирования пуско-тормозных траекторий асинхронных двигателей насосных агрегатов (фиг.5) позволяет устранить возникновение указанных нежелательных режимов, поскольку величина k_I,УП для каждого запускаемого двигателя рассчитывается индивидуально, с учетом соответствующих ограничений. В частности, рассчитанные оптимальные значения коэффициента кратности тока равны: k_опт,i={4,1; 6,2; 4,8}, при этом превышение температуры лобовых частей статорных обмоток АД выше максимально допустимого значения Θ_max,доп=130°С при проведении экспериментов зафиксировано не было.

. An increase in k _{I, UP} to the value of k _{I, UP} = 5 leads to an excess of the maximum pressure increase in the pipeline above the established limit ΔP _{max, by an additional} half. In addition, when the value of k _{I, UP} = 6, a voltage drop occurs in the primary and secondary circuits of the transformer by ΔU _max = 10.1%, which violates the established limitation ΔU _{max, additional} = 10%. The application of the claimed algorithm for adapting the current limiting setpoint for the formation of start-brake trajectories of asynchronous motors of pumping units (Fig. 5) allows eliminating the occurrence of these undesirable modes, since the value of k _{I, UE} for each starting motor is calculated individually, taking into account the corresponding restrictions. In particular, the calculated optimal values of the current multiplicity coefficient are: k _{opt, i} = {4.1; 6.2; 4.8}, while the excess of the temperature of the frontal parts of the stator windings of the blood pressure was higher than the maximum permissible value Θ _{max, additional} = 130 ° C during the experiments was not recorded.

Thus, unlike the prototype, by introducing an additional sequence of procedures for periodically measuring the instantaneous and effective values of the mains voltage and current in the stator windings of an induction motor, calculating the maximum possible current limit setting for the soft starter, and then changing the current value of the current limit setting, it becomes possible to reduce losses electric energy in the windings of induction motors of the pumping unit of the water supply system by hell ptatsii current limit setpoint at a controlled formation of the starting and braking paths. The advantage of the algorithm of the claimed method is the absence of iterations, which allows for sufficient performance for interactive control. On the other hand, in the case of controlling a significant amount of blood pressure at a large pumping station, the structure of the algorithm proposed above for speeding up calculations allows the use of a distributed computer network by parallelizing two groups of the most resource-intensive predictor operations, which is indicated by a dashed line in Fig. 8. For this purpose, it is recommended to use the functions of the additional distributed computing toolbox (Distributed Computing Toolbox), which is part of the SCL "MATLAB 7.4" ^® . In a practical application, the claimed method provides the opportunity to save electricity without changing the structure and composition of the power and control parts of the system "electric network - soft starter - squirrel-cage induction motor - pump - pipeline ”.

Information sources

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Claims (1)

A method of adapting the current limiting setpoint for forming start-brake trajectories of asynchronous motors of pumping units, which consists in the fact that the three-phase voltage is supplied through three pairs of counter-parallel connected thyristors to the stator windings of the asynchronous motor, and control signals from the pulse-phase system are supplied to the control inputs of the thyristors control, synchronized by the current of the stator windings of the induction motor, to the input of which a signal is supplied in the form of a voltage equivalent to the opening angle thyristors, the value of which is set in advance at each moment of time, measure the instantaneous and effective values of the mains voltage and current in the stator windings of the induction motor and, when they deviate from the set values, stop the supply of control signals to the thyristors, characterized in that they also measure instantaneous and effective voltage values network and current in the stator windings of an induction motor and with a frequency determined by the conditions of the water supply process, the state of the electrical network and By the time of computer calculations of the characteristics of the current process of energy conversion in the system "electric network - soft starter - squirrel-cage induction motor - pump-pipe", the maximum possible current limit setting for the soft starter is calculated, during which, during the controlled start of the asynchronous motor, restrictions specified by the technical requirements and change the current value of the current limit setting.

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