Direct current motor constant current braking and hanging object falling speed dynamic control method and control system

Abstract

The invention provides a direct-current motor constant-current braking and hanging object falling speed dynamic control method, which comprises the following steps of: establishing a constant-current parking braking mechanical characteristic equation, establishing a rotating speed / current time-varying model, and replacing a conventional energy consumption braking resistor with a power field-effect tube; the equivalent resistance value between the drain and the source is adjusted on line in a voltage control mode to achieve whole-course constant-current braking of the direct-current motor and dynamic adjustment of the falling speed of the hung object. Theoretical analysis and experimental results show that the method can respectively shorten the parking braking time and the time for stabilizing the falling speed of the hung object under the condition of not changing a hardware system, and the dynamic working efficiency of a motor dragging system and the flexibility of a control system are effectively improved.

Description

Technical Field

[0001] The invention relates to the field of dynamic control of direct current motors, and in particular to a method and a control system for dynamic control of constant current braking of a direct current motor and the falling speed of a suspended object. Background Art

[0003] Rapid parking brake for resistant loads and speed control for potential loads are of great significance to improving the dynamic operation efficiency and production safety of motor traction devices. DC motors have been widely used in electric traction and robot control systems due to their good starting and speed regulation performance, large torque and low influence of electromagnetic interference. DC motors have two operating states: electric and braking. The purpose of motor braking is to quickly stop or decelerate the electric traction system containing resistant loads. For lifting mechanisms containing potential loads, braking can also achieve stable and efficient speed control of suspended objects. DC motor braking methods are generally divided into mechanical braking and electrical braking. Among them, electrical braking includes energy consumption braking, reverse braking and feedback braking. Electrical braking has the characteristics of flexibility, easy controllability and long life, so it has been widely used in the field of automation control. In conventional energy consumption braking, the armature is disconnected from the power supply and connected to a fixed braking resistor to convert the load kinetic energy into electrical energy and consume it on this resistor. It is suitable for both parking brakes for resistant loads and steady-speed drop of potential loads. Reverse braking requires the power supply to be reversed, and a braking resistor must be connected in series in the armature circuit to absorb the load kinetic energy. Its characteristic is that the braking torque is large, and it is suitable for frequent forward and reverse starting and braking. During feedback braking, the potential load drives the motor to generate electricity, and the armature converts the mechanical power of the load on the shaft into electromagnetic power and feeds it back to the power grid. Therefore, it is more economical, but it is difficult to obtain a low drop speed for potential loads.

[0004] The above three electrical braking methods can all be described by clear mechanical characteristic equations. However, the existing braking methods are all based on a fixed braking resistor R z On this basis, the main problems are: (1) For resistant loads, during the system parking brake process, the braking torque will decrease as the motor speed decreases. Since the constant torque braking characteristics cannot be maintained during this period, it is difficult to maximize the braking efficiency. (2) For the drop process of potential energy loads, it takes a long time for the heavy object to reach a stable drop speed from a static state, and without changing the brake system hardware, the heavy object can only be dropped at a fixed stable speed, making it difficult to achieve the control requirements of variable speed drop. Summary of the invention

[0005] The present invention proposes a method and control system for constant current braking of a DC motor and dynamic control of the falling speed of suspended objects. The conventional energy-consuming braking resistor is replaced by a power field effect transistor, and the equivalent resistance between the drain and the source is adjusted online by voltage control. Without changing the system hardware, this method adopts the current and speed dual closed-loop control technology and combines with a digital signal processor to achieve full-range constant current rapid parking braking for resistant loads; for potential loads, it can achieve rapid drop and dynamic adjustment of the falling speed of suspended objects. This braking method can not only effectively improve the dynamic operation efficiency of the motor traction system, but also enhance the flexibility and versatility of the control system.

[0006] The technical solution of the present invention is:

[0007] A method for controlling the constant current braking of a DC motor and the drop speed of a suspended object, which is special in that:

[0008] Step 1: Establish the constant current parking brake mechanical characteristic equation:

[0009]

[0010] Where, T is the electromagnetic torque, T Bmax is the maximum braking torque allowed by the motor, T L is the load torque, n is the motor speed, C T is the torque constant, n c is the turning speed. When the motor speed n drops to n c When n is , the braking torque decreases linearly along the CO straight line segment until the vehicle stops when n is zero. c Determined by formula (2):

[0011]

[0012] In the formula, R a is the armature inherent resistance, C e is the electromotive force constant, is the magnetic flux per pole, I Bmax It is the maximum braking current allowed by the motor for a short time;

[0013] Step 2: Establish a speed / current change model over time

[0014] 2.1 Parking brake time for resistive load

[0015] For the constant current braking method, the braking current is generally kept constant, and the motor speed decreases linearly over time. The motor speed increases from the initial speed n i The total braking time to stop is

[0016]

[0017] To TtM1 and T tM2 After normalization, the above formula can be expressed as

[0018]

[0019] 2.2 Dynamic control of potential load drop speed

[0020] The equivalent resistance between the source and drain of the power MOS tube is dynamically changed by DSP in a voltage-controlled manner to replace the fixed braking resistor R z Ignoring the motor's own rotational inertia, the load falls in a free fall until the system reaches a preset stable speed. The MOS tube turns on and generates a load torque T L Equal electromagnetic braking torque T; when the shaft inertia is ignored, the dynamic process can be expressed as

[0021]

[0022] Take the boundary conditions t = 0, n = 0, then when n = n s When , the solution of the equation group is the time when the hanging object reaches a steady speed drop:

[0023]

[0024] Will and Substitute into formula (16) and normalize

[0025]

[0026] A constant current braking and a dynamic control system for the falling speed of suspended objects adopted by the above-mentioned DC motor constant current braking and the dynamic control method for the falling speed of suspended objects, comprising a DSP, two independent PI adjustment units for current and speed feedback, a power MOS tube T P and a linear optical isolation amplifier, in which the power MOS tube is used as the core unit, and its drain-source is connected to the motor braking circuit. The given speed n of the two PI regulators s And given maximum braking current I Bmax All are set by DSP. The speed feedback is taken from the output of the speed measuring generator TG. The current feedback is fed through the sampling resistor R S The voltage value is obtained indirectly; the current closed loop is used to realize the constant current braking of the resistant load, and the speed closed loop is used to realize the control of the drop speed of the potential load; the output of the two PI regulators acts on the gate of the power MOS tube through the analog multi-way switch and the linear optical isolation amplifier, thereby realizing the function of the voltage-controlled resistor; the channel selection of the analog multi-way switch is controlled by the I / O pin of the DSP; corresponding to the forward and reverse rotation of the motor, the output voltage U of the speed generator TG gtIt has positive and negative properties, so it needs to be added with a positive bias voltage to become a single polarity voltage signal, and then the speed is collected through the built-in AD port of the DSP. t Used to monitor the operating temperature of the power MOS tube in real time.

[0027] The beneficial effect of the present invention is that the present invention replaces the conventional energy-consuming braking resistor with a power field effect transistor, and adjusts the equivalent resistance between the drain and the source online by voltage control to achieve full-range constant current braking of the DC motor and dynamic adjustment of the drop speed of the suspended object. Theoretical analysis and experimental results show that this method can shorten the parking braking time and the time for the suspended object drop speed to reach stability without changing the hardware system, effectively improving the dynamic working efficiency of the motor traction system and the flexibility of the control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the DC motor braking mechanical characteristic curve;

[0029] Figure 2 It is the graph of the braking current changing with time;

[0030] Figure 3 It is a graph showing the relationship between the braking speed and time;

[0031] Figure 4 It is the hardware structure diagram of the motor control system;

[0032] Figure 5 It is the voltage control characteristic diagram of MOS tube Rds;

[0033] Figure 6 This is the circuit diagram of the PI regulator;

[0034] Figure 7 It is the software control algorithm flow chart;

[0035] Figure 8 This is a comparison chart of the relationship between the speed and current changing with time in the traditional parking brake test and the constant current brake test;

[0036] Fig. 9 It is a comparison chart of the change of current and speed over time in the traditional load drop braking experiment and the load drop speed dynamic control experiment. DETAILED DESCRIPTION

[0038] 1. Establishment of mechanical characteristic equations for constant current parking brake and load release

[0039] The so-called constant current parking brake refers to the braking current I in the armature of the motor drag system from the initial braking moment to the entire time period of parking. B It always remains constant and its value is the maximum current I allowed by the motor in a short time. BmaxThe basic principle of the constant current braking proposed by the present invention is to use a power field effect tube drain-source equivalent resistance R ds Replace the fixed resistor R in the conventional energy consumption braking method z , and R ds The value can be adjusted dynamically online through voltage control. The braking mechanical characteristic curve of the motor is as follows: Figure 1 The two reflect the parking brake characteristics of the resistant load and the braking characteristics of the potential load when falling. The BCO solid line segment corresponds to constant current braking; the BO dotted line segment corresponds to conventional energy consumption braking; the O-ns-DE solid broken line segment corresponds to the stable falling speed of the load, which is controllable; the OE dotted line segment corresponds to the stable falling speed of the load, which is fixed. If the electric speed of the motor before braking is n i , because at the initial moment of braking n i The working point moves from point A to point B along the straight line AB, and the motor begins to decelerate due to entering the braking state. For constant current braking, the speed will decrease along the straight line BC, and the braking torque will always remain at the maximum torque -T Bmax When the motor speed n drops to n c When n is 0, the braking torque decreases linearly along the CO straight line segment until the vehicle stops. c is the turning speed, which can be determined by formula (2).

[0040]

[0041] In the formula, R a is the armature inherent resistance, C e is the electromotive force constant, is the magnetic flux per pole, I Bmax It is the maximum braking current allowed by the motor for a short time. c The corresponding value is the motor speed when the MOS tube is fully turned on. At this time, due to the equivalent resistance R between the source and drain of the MOS tube ds The braking current value is no longer controlled by the MOS tube, but depends entirely on the armature's own resistance R a In fact, due to R a Very small, so n c The entire braking process can be approximately regarded as consisting of the constant current section BC. The O-ns-DE section corresponds to the braking mechanical characteristics when the potential energy load is dropped. s The desired stable speed of the motor. When the potential load drops, the motor is driven from a stationary state to a speed n s , passing through the overshoot point D, the final speed stabilizes at n sIt should be noted that the overshoot of the motor speed is caused by the closed-loop speed regulation. The overshoot amount and overshoot time depend on the control algorithm of the regulator and are generally small. Through the above analysis, the mechanical characteristic equation of constant current braking can be expressed as:

[0042]

[0043] Where, T is the electromagnetic torque, T Bmax is the maximum braking torque allowed by the motor, T L is the load torque, n is the motor speed, C T is the torque constant.

[0044] Assume that the conventional energy consumption braking resistor is R z , then the mechanical characteristic equation during braking can be expressed as:

[0045]

[0046] It can be seen that the mechanical characteristic of conventional dynamic braking is a straight line passing through the origin, and the speed n is positively correlated with the electromagnetic torque T, such as Figure 1 As shown in the straight line segment BE.

[0047] 2. Speed / current change over time model

[0048] In order to deeply analyze the constant current braking characteristics, Figure 2 and Figure 3 The relationship between the armature current and the motor speed during the braking process and the time is given respectively. The solid line corresponds to the constant current braking method, and the dotted line corresponds to the conventional energy consumption braking method. The meanings of the relevant symbols in the figure are: t c Indicates the turning point of constant current braking; t o1 With t o2 They represent the parking time corresponding to the constant current braking and conventional energy consumption braking process respectively; t s1 With t s2 They represent the corresponding moments of the two braking methods when the potential load reaches a stable falling speed; n i Indicates the initial speed of the motor; n s Indicates the motor speed when the potential load falls at a steady speed or the set falling speed of the control system; n c It is called transition speed. It should be noted that the origin here represents the initial moment, so each moment also represents the time experienced during the braking process. 2.1 Parking Braking Time for Resistant Load

[0049] from Figure 2 and Figure 3It is not difficult to see that for the constant current braking method, the braking current remains constant overall, and the motor speed generally decreases linearly over time. For the conventional energy consumption braking method, the braking current and motor speed both decrease exponentially over time. Obviously, whether it is parking braking for resistant loads or releasing braking for potential energy loads, the constant current braking efficiency is significantly improved compared with the conventional energy consumption braking efficiency. The fundamental purpose of constant current braking is to stop the motor with resistant loads at the fastest speed under the overcurrent condition allowed by the motor for a short time. The following is a quantitative analysis of the braking time.

[0050] Due to the limitation of mechanical inertia and power carrying capacity, the maximum braking current of the motor is generally taken as twice the rated current, that is, I Bmax =2I N ,T Bmax =2T L First, consider the conventional energy-consuming braking method and transform the motor motion equation T = T L +GD 2 / 375×dn / dt (G is the weight of the rotating part, D is the inertia diameter) is substituted into formula (8), we have

[0051]

[0052] According to formula (8), when T = T L When n=n s , that is, when the transition process ends, the stable speed of the motor is

[0053]

[0054] Combining equation (10) with equation (9), the speed differential equation under conventional dynamic braking can be obtained as follows:

[0055]

[0056] in, is called the electromechanical time constant. The solution to this first-order differential equation is

[0057]

[0058] Depend on Figure 1 From the geometric relationship in n i =-2n s When n = 0, the formula (12) can be used to calculate the speed of the motor from the initial speed n under the conventional energy consumption braking mode. i The braking time to stop is

[0059]

[0060] For the constant current braking method, the motor is i Braking time to stop to1 By Ot c Time period and t c t o1 Time period composition, such as Figure 3 As shown. Among them, Ot c The braking current remains constant during the time period, and as the speed decreases, the drain-source equivalent resistance R of the MOS tube ds During the closed-loop pressure control process, it gradually decreases until it reaches t c At this moment, the MOS tube is fully turned on, and the corresponding speed is n c , that is, the transition speed, its value can be expressed as Combining formula (10) and considering n i =-2n s , get n c With n i The relationship is

[0061]

[0062] In t c t o1 Time period, because the MOS tube is fully turned on, the corresponding on-resistance R ds ≈0, the motor only has the armature winding resistance R a Energy consumption braking is performed under the action of. From the above analysis, we know that Figure 3 Medium constant current braking straight line segment n i C is exactly the conventional energy consumption braking curve n i t o2 Tangent line at time zero. Taking the derivative of both ends of equation (12), we get:

[0063]

[0064] Considering the boundary condition when t=0, n i =-2n s , tangent n i The slope of C is k = -1.50n i / T tM1 The corresponding straight line equation is:

[0065] n=-1.5n i t / T tM1 +n i (16)

[0066] When n=n c When Ot c The time corresponding to the segment is:

[0067]

[0068] Becausec t o1 This section belongs to conventional energy consumption braking. By analogy with formula (13), we can get t c t o1 =1.10T tM2 ,in Combined with formula (17), it can be seen that for the constant current braking method, the motor changes from the initial speed n i The total braking time to stall is:

[0069]

[0070] To T tM1 and T tM2 After normalization, the above formula can be expressed as:

[0071]

[0072] By comparing formula (13) and formula (4), we can draw the following conclusions:

[0073] (1) When the braking resistor R z = 0, t o1 =t o2 =1.1T tM1 In this case, the constant current braking time is the same as the conventional energy consumption braking time, Ot c The time period is 0.

[0074] (2)R z With R a The greater the difference, the longer the constant current braking time t o1 The shorter the conventional energy consumption braking time t o2 . If I Bmax =2I N , then R a +R z =U N / 2I N (U N , I N are the rated voltage and rated current of the motor respectively). Usually R z Greater than 4R a , at this time t o1 Less than 0.75T tM1 , i.e. 0.68t o2 It can be seen that, in theory, the constant current braking method can shorten the parking brake time to at least 68% of the conventional energy consumption braking method, thereby effectively improving the parking brake efficiency of the resistive load.

[0075] 2.2 Dynamic control of potential load drop speed

[0076] If the motor drives a potential load, the mechanical characteristics of the motor will be in the fourth quadrant during the falling process of the suspended object. Figure 1 It can be seen from the mechanical characteristic curve that for the conventional energy consumption braking method, the electromagnetic torque T will gradually increase with the increase of the reverse drop speed of the load until T = T L When the system acceleration is zero, the motor drives the suspended object at n = n s Therefore, for a specific braking resistor R z , the potential load can only be dropped at a single stable speed. The motor drags the load from rest to a stable speed n s The drop time can be obtained by formula (7) in n i = 0. Theoretically, only when t = ∞, n will reach n s , but when t is equal to 3T tM1 When the motor speed reaches n s Therefore, for conventional energy consumption braking methods, the time it takes for the potential load to reach a steady speed from a static state is approximately 3T. tM1 .

[0077] The present invention uses DSP to dynamically change the equivalent resistance between the source and drain of the power MOS tube in a voltage-controlled manner to replace the fixed braking resistor R z Without changing the hardware, the motor can realize rapid drop control of the potential load and dynamic adjustment of the stable drop speed. Figure 2 and Figure 3 t o1 -t s1 The time period corresponds to the process of dropping the hanging object, t o1 is the stationary moment, t s1 This is the moment when the steady speed is reached. During this period, the power MOS tube is completely turned off, and the armature circuit current I a and braking torque T are both zero, so the load falls in a free fall manner while ignoring the motor's own rotational inertia. When the system reaches the preset stable speed, the MOS tube turns on and generates the same torque as the load torque T. L Equal electromagnetic braking torque T. When the shaft inertia is ignored, the dynamic process can be expressed as

[0078]

[0079] Take the boundary conditions t = 0, n = 0, then when n = n s When , the solution of the equation group is the time when the hanging object reaches a steady speed drop.

[0080]

[0081] In order to facilitate comparison with conventional energy consumption braking methods, and Substitute into formula (6) and normalize

[0082]

[0083] It can be seen that the dynamic control method of falling speed can not only realize the dynamic control of the stable falling speed of the potential energy load, but also shorten the time for the suspended object to reach a stable falling speed to 1 / 3 of the conventional energy consumption braking method, effectively improving the versatility and efficiency of the motor traction system.

[0084] A constant current braking and hanging object falling speed dynamic adjustment system, such as Figure 4 As shown, it mainly consists of two independent PI adjustment units for current and speed feedback, power MOS tube T P The power MOS tube is the core component, and its drain-source is connected to the motor braking circuit. The given speed n of the two PI regulators s And given maximum braking current I Bmax All are set by DSP program. The speed feedback is taken from the output of the speed measuring generator TG. The current feedback is obtained through the sampling resistor R S The voltage value is obtained indirectly. The current closed loop is used to achieve constant current braking of the resistive load, while the speed closed loop is used to control the drop speed of the potential load. The output of the two PI regulators acts on the gate of the power MOS tube through the analog multi-way switch and the linear optical isolation amplifier, thereby realizing the function of the voltage-controlled resistor. The channel selection of the analog switch is controlled by the I / O pin of the DSP. Corresponding to the forward and reverse rotation of the motor, the output voltage U gt It has positive and negative properties, so it needs to be added with a positive bias voltage to become a single polarity voltage signal, and then the speed is collected through the built-in AD port of the DSP. The signal isolation unit can be composed of a transformer or a linear optocoupler amplifier, and the thermistor R t Used to monitor the operating temperature of the power MOS tube in real time.

[0085] Both constant current braking and dynamic control of the falling speed of suspended objects are based on the voltage-controlled variable resistance characteristics of power MOS tubes. Figure 5 As shown, when its gate-source voltage V gs Less than the threshold voltage V th When the source-drain resistance R ds =∞, when V gs Greater than the turn-on voltage V on When R ds ≈0, and when V th <V gs <V on When R ds Varies continuously between 0 and ∞.

[0086] The working state of the motor can be determined by detecting the switch SW through the DSP I / O port. When it is closed, the analog multiplexer selects the CH3 channel. At this time, T P Because V gs <V th When it is cut off, the motor works in the forward motoring state; when it is disconnected, the analog multi-way switch selects channel CH1. At this time, T P The gate of the motor is in a constant current braking state because it is controlled by the output end of the current PI regulator 1.

[0087] The working process of constant current braking is as follows: (1) I Bmax After the built-in D / A conversion and inverter of DSP, it is converted into a voltage U proportional to it. ig =kI Bmax (k is a negative number), and from the sampling resistor R S The voltage obtained is passed through an inverter and an optical isolation amplifier to obtain a feedback voltage U proportional to the braking current. if , its value is positive. Figure 6 The circuit structure of PI regulator 1 and PI regulator 2, where the output voltage of PI regulator 1 can be expressed as

[0088]

[0089] (2) The output U0 of the PI regulator is selected by a multi-way switch and amplified by a linear optical amplifier to realize the control of T P Equivalent resistance R ds When the actual braking current I B Less than the given current I set by the program Bmax When U if <|U ig |. Due to the integral effect, U0 is greater than 0 and continues to increase, resulting in R ds Continuously decreasing, I B Gradually increase until I B =I Bmax U0 tends to be stable only when ds Also stabilized at a certain value, the motor is in constant current braking state, corresponding to Figure 2 and Figure 3 Ot c part.

[0090] The speed control of the potential load is mainly through the speed PI regulator 2, the speed generator TG and the power MOS tube T P The specific process is: when DSP detects that the motor braking speed drops to 0, it switches the analog multiplexer to the CH2 channel. At this time, the stable falling speed of the hanging object set by the program is converted into the corresponding given voltage U by the D / A converter. ng, this voltage is proportional to the feedback voltage U output by TG and is proportional to the speed nf Because the motor reverses when the hanging object is dropped, the TG output voltage U nf is negative, so the output voltage of PI regulator 2 can be expressed as

[0091]

[0092] U0 is selected by a multi-way switch and amplified by an isolator to realize T P Equivalent resistance R ds From formula (19), it can be seen that when the feedback speed is lower than the given speed, it is equivalent to |U nf | ng When U0 is negative, T P The braking current and braking torque are 0, and the hanging object falls with the acceleration of gravity. Figure 2 and Figure 3 t in o1 -t s1 As the falling speed of the hanging object increases, |U nf |Increase, when it is slightly greater than U ng When U0 is positive, T P Starts to conduct so that I B Rapidly increases. At this time, the acceleration of the suspended object gradually decreases due to braking. Finally, when |U nf |=U ng When R ds and I B The braking torque is equal to the load torque, so the object falls at a constant speed according to the system's given speed. The given speed n can be reset by software during the falling process. s To achieve dynamic adjustment of the falling speed of suspended objects.

[0093] Software Algorithm

[0094] Software control algorithms such as Figure 7 As shown in Figure 1, it consists of a main program and an interrupt service program. The main program has the following functions: (1) DSP register initialization; (2) setting the motor braking current value I Bmax (with U ig Corresponding) and the stable falling speed n of potential load s (with U ng (3) The detection switch SW is used to determine whether the motor is in the electric or braking state, and accordingly to switch the channels of the analog multi-way switch. The interrupt service program is used to detect the temperature of the power MOS tube in real time, so as to provide over-temperature alarm and protection for the controller.

[0095] System simulation experiment

[0096] 1. Simulation parameter setting and performance comparison​

[0097] In order to verify the effectiveness of the above constant current braking and load drop speed control method, the present invention uses the internationally recognized Multisim simulation tool to experimentally verify the above theory. Figure 8-Figure 9 Four typical comparison test results are given, and the corresponding motor parameters are: speed 9258rpm, shaft inertia 0.015kg.m2, armature inductance 0.1mH, armature resistance 0.2Ω, I N =12.5A, U N =80V,I Bmax =25A. Among them, Figure 8 The relationship between the speed / current and time corresponding to the conventional energy consumption braking method and the constant current braking method; Fig. 9 The relationship between the speed / current and time corresponding to the conventional control method and the speed dynamic adjustment method for potential load drop is shown in Figure 2. It is easy to see that the synthetic waveform of the above four groups of experimental curves is consistent with Figure 2 , Figure 3 The corresponding theoretical analysis results are consistent, which qualitatively illustrates the correctness of the above motor braking theory.

[0098] 2. Quantitative analysis of experimental results

[0099] In order to fully evaluate the accuracy of the theoretical model, it is necessary to further conduct diversified quantitative experiments. Table 1 is based on the results of Sharftinertia = 0.015 kg.m 2 , the motor stopping time is measured by two different braking methods under the condition that the braking current is twice the rated current. i is the initial speed of the motor, T L is the load torque, U N is the rated voltage of the motor, I N is the rated current of the motor, t B is the constant current parking brake time, t N is the conventional energy consumption parking brake time, η P t B With t N The results show that η P The minimum and maximum values ​​are 65.0% and 67.3% respectively, which are consistent with the theoretical value of 66.6%, and the relative error is less than 2.5%.

[0100] Table 1 Comparison of parking time of two motor braking methods under different parameters

[0101]

[0102] Table 2 is the result of Sharftinertia = 0.005, T L =0.5Nm, n i= 0, the time it takes for the potential load to drop from rest to steady speed measured by the two methods. s To stabilize the drop current, t f The time it takes for the suspended object to reach a steady speed from rest corresponding to the speed dynamic adjustment method, t n The time for the load to reach 95% of the steady speed from rest corresponding to the conventional braking method, η d t f With t n The results show that η d The minimum and maximum values ​​are 33.1% and 33.7% respectively, which are in good agreement with the theoretical value of 33.3%, and the relative error is less than 1.2%.

[0103] Table 2 Comparison of working efficiency of two methods of hanging object falling speed control under different parameters

[0104]

[0105] The present invention proposes a method for constant current braking and dynamic control of the falling speed of a DC motor, in which a power field effect tube replaces a conventional energy-consuming braking resistor. Based on this, the mechanical characteristic equation of the system is established, and the relationship between the motor speed and the armature current over time during the constant current parking braking and the falling of the hanging objects is systematically analyzed. The model shows that the constant current braking method can shorten the parking time to at least 66.7% of the conventional energy-consuming braking method; the falling speed dynamic control method can not only realize the continuous adjustment of the falling speed of the potential load, but also shorten the time for the hanging object to reach a stable falling speed to 33.3% of the conventional energy-consuming braking method. On this basis, the hardware circuit and software algorithm of the system are designed to prove the technical feasibility of the constant current braking and falling speed dynamic control method proposed in the present invention. Through diversified simulation experiments under different parameter combinations, the correctness of the motor braking theory proposed in the present invention is fully proved from both qualitative and quantitative perspectives. The implementation of this method can effectively improve the dynamic working efficiency of the DC motor traction system, and at the same time, it also helps to enhance the versatility of the motor control system.

Claims

1. A method for controlling the constant current braking of a DC motor and the drop speed of a suspended object, characterized in that: S1. Establish the constant current parking brake mechanical characteristic equation: Where, T is the electromagnetic torque, T Bmax is the maximum braking torque allowed by the motor, T L is the load torque, n is the motor speed, C T is the torque constant, n c is the turning speed. When the motor speed n drops to n c When n is , the braking torque decreases linearly along the CO straight line segment until the vehicle stops when n is zero. c Determined by formula (2): In the formula, R a is the armature inherent resistance, C e is the electromotive force constant, is the magnetic flux per pole, I Bmax It is the maximum braking current allowed by the motor for a short time; S2. Establish a speed / current change model over time S2.1 Parking brake time for resistive load For the constant current braking method, the braking current is generally kept constant, and the motor speed decreases linearly over time. The motor speed increases from the initial speed n i The total braking time to stop is To T tM1 and T tM2 After normalization, the above formula can be expressed as: S2.2 Dynamic control of potential load drop speed The equivalent resistance between the source and drain of the power MOS tube is dynamically changed by DSP in a voltage-controlled manner to replace the fixed braking resistor R z Ignoring the motor's own rotational inertia, the object falls in a free fall manner until it reaches the stable speed preset by the system, and the MOS tube turns on and generates a load torque T L Equal electromagnetic braking torque T; when the shaft inertia is ignored, the dynamic process can be expressed as: Take the boundary conditions t = 0, n = 0, then when n = n s When , the solution of the equation group is the time when the hanging object reaches a steady speed drop: Will and Substitute into formula (16) and normalize:

2. A constant current braking and a dynamic regulating system for the falling speed of suspended objects adopted by the above-mentioned method for constant current braking of a DC motor and dynamic control of the falling speed of suspended objects, characterized in that: Including DSP, two independent PI regulation units for current and speed feedback, power MOS tube T P and linear optical isolation amplifier, in which the power MOS tube is used as the core component unit, and its drain-source is connected to the motor braking circuit. The given speed n of the two PI regulators s And given maximum braking current I Bmax All are set by DSP. The speed feedback is taken from the output of the speed measuring generator TG. The current feedback is fed through the sampling resistor R S The voltage value is obtained indirectly; the current closed loop is used to realize the constant current braking of the resistive load, and the speed closed loop is used to realize the control of the drop speed of the potential load; the output of the two PI regulators acts on the gate of the power MOS tube through the analog multi-way switch and the linear optical isolation amplifier, thereby realizing the function of the voltage-controlled resistor; The channel selection of the analog multiplexer is controlled by the I / O pin of the DSP; corresponding to the forward and reverse rotation of the motor, the output voltage U of the tachogenerator TG gt It has positive and negative properties, so it needs to be added with a positive bias voltage to become a single polarity voltage signal, and then the speed is collected through the built-in AD port of the DSP. The thermistor Rt is used to monitor the operating temperature of the power MOS tube in real time.

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