Non-inductive control method for electric mechanism

Abstract

The invention discloses a non-inductive control method for an electric mechanism, and relates to the technical field of control or adjustment of motors, in particular to control or adjustment of motors, generators or electromechanical converters. According to the technical scheme, the non-inductive control method for the electric mechanism is characterized by comprising the following steps that S1, a counter electromotive force zero-crossing detection method under multiple PWM modulation modes is analyzed, and an accurate expression of suspension counter electromotive force under the multiple PWM modulation modes under different operation conditions is obtained; s2, obtaining the moment when the counter electromotive force crosses the zero point according to the obtained expression, and carrying out time delay to obtain a commutation signal of the motor; s3, performing commutation control on the motor to run stably according to the power-on sequence; and S4, the electric energy storage mechanism realizes accurate and rapid switching-on and switching-off of the equipment. The problems of much interference, low stability, poor accuracy and the like are solved, and the purposes of high precision, comprehensiveness, accuracy, interference removal and high stability are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of control or regulation of electric motors, and in particular to control or regulation of electric motors, generators or electromechanical converters. Background Art

[0002] Due to the development of new power systems, the goal of building a smart grid is also gradually being achieved. With the update and iteration of power equipment and switch devices, devices with remote control functions will become the mainstream of the power system. Motor drive, green and environmentally friendly, has been used as an auxiliary closing device on some devices and equipment, and will play a huge role as an operating mechanism on high-voltage circuit breakers, switch cabinets and other equipment. Because the power supply is a DC power supply, the motors used in the electric operating mechanism of the existing equipment are mostly DC motors, which have the disadvantages of short life and easy sparks due to the friction of carbon brushes and commutators. The brushless DC motor has no components such as carbon brushes and commutators, low noise, long life, high reliability and anti-interference, and is the preferred driving device for the electric mechanism of power equipment. In addition, the brushless DC motor with sensorless control is smaller in size and can withstand harsh environments because it is not equipped with a position sensor. The life and reliability are further improved, and the application range is wider. Since power equipment is often exposed to open air environments, it is very susceptible to corrosion interference from various factors, and the existing sensorless control strategy has certain defects. Therefore, this patent focuses on discussing and proposing a new sensorless control strategy for the electric mechanism of power equipment. The terminal voltage method is often used for the sensorless control of brushless DC motors: the back electromotive force zero-crossing point information is extracted from the terminal voltage to control the motor commutation operation. Usually, the 1 / 2 DC bus side voltage is used as the neutral point voltage, and the suspended back electromotive force zero-crossing detection method with 1 / 2 DC bus voltage as the neutral point voltage is called the terminal voltage direct comparison method. For example, the Chinese patent with publication number CN117856688A discloses a sensorless control method, a storage medium and a frequency conversion controller, and provides the following technical solutions. The embodiments of the present application provide a sensorless control method, a storage medium and a frequency conversion controller, which relate to the field of motor control technology. The sensorless control method obtains the total back electromotive force based on the estimation of the γ-axis back electromotive force component and the δ-axis back electromotive force component; then obtains the estimated position based on the back electromotive force constant; and obtains the estimated speed based on the differential of the estimated position in time. This non-sensing control method uses the total back electromotive force to calculate the position instead of the tan-1 function of the back electromotive force component of the d-axis and the back electromotive force component of the q-axis, thereby avoiding the large error caused by the small back electromotive force component of the d-axis and the back electromotive force component of the q-axis in the low-frequency driving range, and thus can achieve high-precision control in the low-frequency driving range. However, the above-mentioned non-sensing control method, storage medium and frequency conversion controller do not consider the situations under various PWM modulation modes, and do not consider the interference caused by various situations such as the freewheeling state. Summary of the invention

[0003] In view of the problems of much interference, low stability and poor accuracy mentioned in the background technology, the present invention proposes a sensorless control method for an electric mechanism, which achieves the goals of high accuracy, comprehensiveness, simplicity and reliability.

[0004] To achieve the above object, the present invention adopts the following technical solution: A sensorless control method for an electric mechanism, characterized by comprising the following steps: S1: Analyze the back EMF zero-crossing detection method under several PWM modulation modes, and obtain the precise expression of the suspended back EMF under various PWM modulation modes under different operating conditions; S2: Obtain the moment when the back electromotive force crosses zero according to the obtained expression, and obtain the commutation signal of the motor by delay; S3: Control the motor to run smoothly according to the power-on sequence; S4: The electric energy storage mechanism enables accurate and rapid opening and closing of the equipment.

[0005] The advantage of this design is that accurate back-EMF zero-crossing detection can be achieved by analyzing the expressions of the suspended back-EMF under different PWM modulation modes and different working conditions. At the same time, the motor's commutation signal can be obtained by delaying the zero-crossing moment, and combined with the power-on sequence, non-sensing control can be achieved, improving the working efficiency and performance of the electric mechanism. Finally, the smoothly running motor drives the electric energy storage mechanism to open and close, realizing the control and adjustment of the on-off state.

[0006] Preferably, the step S1 and the step S2 include analysis of a situation in which the intermittent flow associated with suspension is not considered and analysis of a situation in which the intermittent flow associated with suspension is considered.

[0007] The advantage of this design is that by analyzing the situation without considering the intermittent current related to suspension and the situation considering the intermittent current related to suspension, the working principle and influencing factors of the electric mechanism non-sensing control method can be more comprehensively understood and analyzed. At the same time, by selecting the corresponding analysis method according to the specific situation, the expression of the opposite potential of suspension can be obtained more accurately, and the accuracy and reliability of non-sensing control can be improved.

[0008] Preferably, in step S1, the analysis of the situation of not considering the suspension-related intermittent flow includes the following steps: S1.1: Determine whether the upper and lower bridge arms are complementary and turned on. If so, set the dead time and proceed to step S1.2. If not, proceed to step S1.2; S1.2: According to the PWM signal of the chopping in each cycle being in the high-level on state and the low-level off-state and the end of the low-level freewheeling, the corresponding motor voltage equation is obtained, and the corresponding suspended opposite potential expression is calculated and enters step S2.

[0009] The advantage of this design is that by judging whether the upper and lower bridge arms are complementary and conducting and calculating the motor voltage equation, the expression of the suspended opposite electromotive force can be obtained, and then the exact moment when the back electromotive force crosses zero can be calculated, thereby improving the accuracy and stability of the sensorless control.

[0010] Preferably, in step S1, the analysis of the situation of considering the suspension-related intermittent flow includes the following steps: S1.3: According to the PWM signal of the chopping wave in each cycle being in the high-level conduction state, the low-level shutdown freewheeling state and the low-level freewheeling end state, the corresponding motor voltage equation is obtained, and the expression of the suspended opposite potential is calculated; S1.4: Based on the principle of solving differential equations, the expression of the suspended phase freewheeling current and freewheeling time are obtained; S1.6: The freewheeling time is obtained by comparing whether the suspended phase voltage is greater than the DC bus voltage or less than zero; S1.7: Obtain the corresponding freewheeling end time according to the complementary conduction of the upper and lower bridge arms, and enter step S2.

[0011] The advantage of this design is that by considering the analysis of the intermittent current related to the suspension, the back-electromotive force expression and the continuous current time of the suspended phase can be calculated more accurately, and the occurrence and end time of the continuous current can be determined, thereby improving the accuracy and reliability of the non-sensing control.

[0012] Preferably, the step S1.7 comprises the following steps: S1.71: Determine whether the upper and lower bridge arms are complementary and conductive. If so, proceed to step S1.8; if not, proceed to step S1.9; S1.72: Set the dead time, and use the timer to count the duration that the suspended phase voltage is greater than the DC bus voltage or less than zero to obtain the moment when the freewheeling ends, and then go to step S2; S1.73: The moment when the freewheeling ends is obtained by calculating the freewheeling time or by timing the duration of the suspended phase voltage being greater than the DC bus voltage or less than zero through a timer, and then proceeding to step S2.

[0013] The advantage of this design is that by judging the conduction conditions of the upper and lower bridge arms and the duration of the end of the timing of the freewheeling, the moment when the freewheeling ends can be accurately determined, and the commutation control of the motor can be further realized.

[0014] Preferably, in step S2, considering the case of suspended intermittent flow, the following steps are included: S2.1: Compare the back electromotive force time corresponding to the electrical angle of 30° with the freewheeling time to determine the effect of freewheeling on the acquisition of the zero-crossing point; S2.2: Determine whether the continuous flow ends before the back electromotive force crosses zero. If so, proceed to step S2.3; if not, proceed to step S2.4; S2.3: Use reasonable voltage threshold and digital filtering to remove interference, refer to the suspended related continuous flow conditions, select the corresponding back electromotive force expression in combination with the actual situation, or directly obtain the back electromotive force zero crossing point based on the back electromotive force expression, and proceed to step S2.5; S2.4: Obtain the back electromotive force zero crossing point based on the back electromotive force expression; S2.5: Get the accurate back EMF zero-crossing point, delay 30° electrical angle to get the commutation signal, and go to step S3.

[0015] The advantage of this is that, by analyzing the freewheeling time and the zero-crossing point of the back-EMF, the corresponding back-EMF expression can be selected according to the actual situation, and the timing of the commutation signal can be accurately determined to achieve sensorless control of the motor.

[0016] Preferably, in step S2, the case of suspended intermittent current is not considered, and the corresponding suspended back electromotive force expression is selected according to the parameters and state of the circuit to obtain the moment when the back electromotive force passes through zero, and the motor commutation is controlled by delaying 30° electrical angle.

[0017] The advantage of this design is that the expression of the suspended opposite electromotive force can be flexibly selected according to the parameters and status of the circuit to achieve accurate commutation control of the motor.

[0018] Preferably, the step S2 includes removing the remaining part of the zero-crossing interference pulse and fine-tuning the commutation signal through a fixed-delay digital filter, and obtaining the final commutation signal through post-processing.

[0019] The advantage of this design is that by removing the remaining part of the interference pulse and fine-tuning the commutation signal through the digital filter, a more accurate and stable commutation signal can be obtained, thereby improving the accuracy and reliability of the sensorless control.

[0020] Preferably, the dead time is set to 1 to 2 us.

[0021] Preferably, the back electromotive force expression is: e=at+E.

[0022] Compared with the prior art, the invention has the following beneficial effects.

[0023] 1. The present invention considers using a brushless DC motor with sensorless control as the driving motor of the energy storage mechanism of the power equipment, so that: ① the power equipment can adapt to relatively harsh operating conditions, enhancing the adaptability of the system. ② the energy storage mechanism of the power equipment is smaller in size, longer in life, and less noisy.

[0024] 2. By accurately analyzing the expressions of the suspended back electromotive force under different PWM modulation modes and different operating conditions, including the cases without considering the suspended related intermittent current and the cases considering the suspended related intermittent current, the accurate back electromotive force zero crossing point is obtained for motor commutation, which helps the motor to run smoothly and reliably, so that the electric mechanism of the power equipment can operate correctly and quickly.

[0025] 3. The present invention avoids the phase delay compensation and wiring complexity caused by the introduction of filters, simplifies the process of obtaining the zero-crossing point of the back electromotive force, reduces hardware costs and dependence on high-performance devices, and improves reliability. By setting a reasonable voltage threshold and digital filtering to remove interference, the system's resistance to noise and interference is improved, and the system's robustness is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart for analyzing the situation of the present invention without considering the suspension-related intermittent flow.

[0027] Figure 2 The present invention is a flow chart of analyzing the situation of suspended related intermittent flow.

[0028] Figure 3 This is the equivalent structural model diagram of the motor of the present invention.

[0029] Figure 4 This is the principle diagram of the low-pass filtering back electromotive force method of the present invention.

[0030] Figure 5 This is a comparison diagram of the reverse potential waveform and the commutation signal of phase A of the present invention.

[0031] Figure 6 It is a schematic diagram of A+B- conduction during the high level period of the present invention.

[0032] Figure 7 It is a schematic diagram of the continuous flow of phases A and B during the shutdown period of the present invention.

[0033] Figure 8 It is a schematic diagram of the conduction state of the switch tube of the present invention.

[0034] Fig. 9 It is a schematic diagram of the conduction of V1 and V6 under H-PWM_L-PWM modulation of the present invention.

[0035] Fig.10 It is a schematic diagram of the suspended phase flow of the present invention.

[0036] Fig.11 This is a waveform diagram of the commutation signal and back-electromotive force of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present disclosure clearer, the following will further describe the embodiments of the present disclosure in detail with reference to the accompanying drawings. The proportions of the components are not drawn according to the actual proportions, and the proportions and sizes shown in the accompanying drawings should not limit the substantial technical scheme of the present invention. These embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described.

[0038] See also Figure 1-11 As shown, a sensorless control method of an electric mechanism is characterized by comprising the following steps: S1: Analyze the back EMF zero-crossing detection method under several PWM modulation modes, and obtain the precise expression of the suspended back EMF under various PWM modulation modes under different operating conditions; S2: Obtain the moment when the back electromotive force crosses zero according to the obtained expression, and obtain the commutation signal of the motor by delay; S3: Control the motor to run smoothly according to the power-on sequence; S4: The electric energy storage mechanism enables accurate and rapid opening and closing of the equipment.

[0039] like Figure 1 and Figure 2 The flowchart of the method of the present invention is shown in FIG. The steps of the sensorless control method of an electric mechanism of the present invention can be summarized as follows: First, in step S1, a detailed analysis of the back EMF of the suspended phase under various PWM modulation modes is carried out, and different operating conditions are considered to obtain an accurate back EMF expression. This step involves two situations: one is not considering the intermittent flow related to the suspension (steps S1.1 and S1.2), and the other is considering this situation (steps S1.3 to S1.7). In the analysis without considering the intermittent flow, it is necessary to determine whether the upper and lower bridge arms are complementary to each other, set the dead time, and then calculate the back EMF expression of the suspended phase. In the case of considering the intermittent flow, in addition to calculating the back EMF, it is also necessary to obtain the freewheeling current expression and the freewheeling time according to the principle of differential equations, and determine the occurrence and end time of the freewheeling by comparing the voltage.

[0040] Next, in step S2, based on the expression obtained in S1, the zero-crossing moment of the back EMF can be obtained, and a delay is set to obtain the commutation signal of the motor. This step also includes two cases: considering (steps S2.1 to S2.5) and not considering (the rest of step S2) the suspended related intermittent flow. Without considering the intermittent flow, by selecting a suitable back EMF expression, the zero-crossing moment is obtained and the commutation control is delayed by 30° electrical angle. When considering the intermittent flow, it is necessary to judge the impact of the continuous flow on the acquisition of the zero-crossing point, and obtain accurate zero-crossing and commutation signals through appropriate digital filtering and threshold setting.

[0041] Step S3 involves commutating the phases according to the power-on sequence to control the smooth operation of the motor, while step S4 is to achieve accurate and rapid opening and closing of the equipment through the electric energy storage mechanism.

[0042] In the process of determining in detail whether the upper and lower bridge arms are complementary turned on, the dead time is set to 1 to 2 microseconds (step S1.71) so as to facilitate timing and determining the end time of the freewheeling through the timer (steps S1.72 and S1.73).

[0043] Step S2 also includes using a fixed delay digital filter to remove the remaining part of the zero-crossing interference pulse and fine-tuning the commutation signal to facilitate post-processing to obtain the final commutation signal.

[0044] Finally, after step S2, the introduced back-electromotive force expression is e=at+E, which is used to calculate the back-electromotive force zero-crossing point and assist in the generation of the commutation signal.

[0045] In summary, the sensorless control method comprehensively considers the PWM modulation mode, the intermittent flow influence of the suspended phase, the complementary conduction judgment and the dead time setting, and ensures the accuracy and efficiency of the sensorless control of the electric mechanism through precise algorithms and control strategies.

[0046] With the development of new power systems, the goal of building a smart grid is gradually being achieved. With the update and iteration of power equipment and switch devices, devices with remote control functions will become the mainstream of the power system. Motor drive, which is green and environmentally friendly, has been used as an auxiliary closing device on some devices and equipment, and will play a huge role as an operating mechanism on high-voltage circuit breakers, switch cabinets and other equipment. Because the power supply is a DC power supply, the motors used in the electric operating mechanisms of existing equipment are mostly DC motors, which have the disadvantages of short life and easy spark generation due to friction between carbon brushes and commutators. Brushless DC (BLDC) motors not only have simple control methods, high efficiency, excellent speed regulation performance, and high power density, but also do not have the problems of sparks and noise caused by mechanical commutation [1]. They are widely used in various fields such as automotive electronics, automation, and aerospace.

[0047] Brushless DC motors usually use Hall position sensors for position detection, but the existence of position sensors limits the use environment of brushless DC motors, as shown in the following.

[0048] (1) The position sensor may not work properly in harsh environments such as high temperature, high dust, high humidity, and highly corrosive gases.

[0049] (2) The presence of the position sensor increases the size of the motor, limits the use scenarios of the motor, and makes maintenance inconvenient.

[0050] (3) The presence of the position sensor requires more wiring for the motor, which increases the difficulty of installing the entire machine; when the Hall signal lead is close to the three-phase power lead, it is easy to introduce interference, increasing the failure rate and working unreliability of the control system.

[0051] (4) The position sensor is the most vulnerable to damage in the entire motor system, and due to its installation location, once damaged, the entire motor must be replaced, which results in high maintenance costs.

[0052] In summary, the sensorless control of brushless DC motors can withstand the influence of harsh environmental factors, have a wider range of application scenarios, lower costs, and do not make the wiring too complicated. They are particularly suitable for installation in switch cabinets, high-voltage circuit breakers and other equipment. The most commonly used strategy for sensorless control of brushless DC motors is the back-EMF method, which mainly includes the terminal voltage detection method and the line back-EMF method [8]. The terminal voltage detection method is a method in which the back-EMF zero crossing point and position signal obtained by comparing the terminal voltage or the processed terminal voltage signal with the neutral point voltage are used for motor commutation.

[0053] Usually, the floating opposite potential zero-crossing detection method with 1 / 2 DC bus side voltage as the neutral point voltage is called the terminal voltage direct comparison method.

[0054] In order to obtain a more accurate zero-crossing signal under interference such as freewheeling and PWM chopping, and avoid the phase delay problem caused by low-pass filtering, the present invention proposes a new zero-crossing detection method, namely the improved terminal voltage method, after analyzing the suspended opposite potential zero-crossing information in various freewheeling states under 8 common PWM modulation modes and deriving related expressions.

[0055] The improved terminal voltage method proposed in the present invention refers to a method for obtaining the motor back-electromotive force zero-crossing information and rotor position by comparing the motor three-phase terminal voltage signal with the neutral point voltage and combining the current operating state without constructing a simulated neutral point and using a filter. Specifically, for different operating conditions, the corresponding expression is selected to obtain the zero-crossing information. At the same time, the back-electromotive force expression during freewheeling and chopping and the tube voltage drop and fixed delay of the conducting diode are used to weaken the interference of factors such as PWM chopping and freewheeling during zero-crossing detection. This method is simple and feasible, and there is no need to perform filter phase delay compensation. The complexity of the motor peripheral wiring is greatly reduced, and the detection reliability is improved. It is particularly suitable for power equipment with electric operating mechanisms such as high-voltage circuit breakers and switch cabinets.

[0056] like Figure 3As shown in the figure, it is an equivalent model diagram of a brushless DC motor with three-phase star connection and two-phase conduction of 120°. The following assumptions are made for the brushless DC motor model: 1) Ignore various losses and magnetic circuit saturation factors; 2) The three-phase winding is symmetrical

[11] ; 3) The winding inductance is a constant

[12] . Then the motor three-phase voltage equation is as follows: In the formula, u a 、u b 、u c is the terminal voltage of the three-phase winding (V); i a 、i b 、i c is the phase current of the three-phase winding (A); e a 、e b 、e c is the back EMF of the three-phase winding (V); u n is the neutral point voltage (V); L represents the equivalent inductance (H); p is the differential operator, p = d / dt.

[0057] At present, the most common method of back electromotive force method is to use a low-pass filter to filter the terminal voltage, and use a resistor network to reconstruct the neutral point and compare the zero-crossing information. The schematic diagram is as follows: Figure 4 The specific method is to set the motor three-phase terminal voltage u a 、u b 、u c The signal is sent to a hardware low-pass filter, and the filtered signal is compared with the neutral point potential for zero crossing to obtain the corresponding high and low levels, which are sent to the microcomputer (MCU) for delay compensation and generate corresponding commutation signals. However, this approach has problems such as complex wiring, complex phase delay compensation and calculation (delay compensation involves inverse trigonometric function calculation or table lookup method), and neutral point potential drift caused by three-phase asymmetry, which affects the accuracy and reliability of commutation.

[0058] In order to further reduce complexity, improve reliability and cost-effectiveness, 1 / 2 of the bus-side DC voltage is directly used as the neutral point voltage for zero-crossing comparison or zero-crossing detection is performed during the off period of the PWM signal. This approach is reasonable to a certain extent, but it also has certain errors.

[0059] like Figure 5The figure shows the back EMF waveform and commutation signal comparison diagram obtained by the direct comparison method of the terminal voltage under Hall inductive control at a speed of 1500r / min, and a load of 2Nm is applied at 0.5s. The back EMF waveform obtained by the direct comparison method of the terminal voltage under Hall inductive control has interference from the freewheeling and PWM chopping, and the back EMF expression is inaccurate, resulting in the commutation signal having a zero-crossing error jump. However, the commutation signal cycle obtained by the direct comparison method of the terminal voltage and the first high-level jump moment (without considering the influence of freewheeling, etc.) are basically consistent with the relevant information of the commutation signal obtained by the Hall sensor. It can be seen that by improving the direct comparison method of the terminal voltage, a simple, feasible and relatively accurate back EMF zero-crossing detection method without a filter can be obtained. Based on this, the present invention derives and analyzes the suspended back EMF equation under a variety of common PWM modulation modes, focusing on analyzing a variety of situations in the freewheeling process, and obtaining relatively accurate zero-crossing information.

[0060] (1) Without considering the intermittent current related to the suspension, the back EMF zero-crossing detection method under several PWM modulation modes is analyzed and summarized. First, the H-PWM_L-PWM modulation mode is analyzed. The schematic diagram of the circuit when the upper bridge arm of phase A is turned on (A+) and the lower bridge arm of phase B is turned on (B-) is shown in the figure. Figure 6 As shown. In the following text, the conduction condition is represented by a certain phase + a certain phase -, and no text is used to express it. The arrows in the figure represent the direction of current flow, which is the same as the following text and will not be repeated.

[0061] ①Assuming that in the A+B- conduction mode, when the PWM signal is at a high level, the motor voltage equation is as follows: During this period, phase C is suspended, ic=0, and at the same time ib=-ia, ea=-eb. Then, by adding equations ua and ub, we can get equation (3), and substituting them into the terminal voltage equation of uc, we get equation (4).

[0062] ② During the PWM signal off period, the A and B two-phase continuous current diagram is as follows Figure 7 As shown, the motor voltage equation during freewheeling is: From this we can also get formulas (3) and (4).

[0063] ③After the continuous current ends, it enters an uncertain state, such as Figure 4 shown.

[0064] Similarly, similar analysis can be performed on the other PWM modulation modes. Taking phase C as the suspended phase, ignoring the device conduction voltage drop, and not considering the condition of the suspended phase continuous current, the expressions of the suspended phase potential under different PWM modulation modes can be obtained as shown in Table 1.

[0065] Table 1 Expression of the suspended opposite potential under different PWM modulation modes There are several explanations for Table 1: ① When the suspended phase is phase C, A+B- is turned on or B+A- is turned on, so there are multiple expressions corresponding to several different situations.

[0066] ② Assume that the back EMF waveform is an ideal 120° flat-top wave.

[0067] ③ Since the upper and lower bridge arms are complementary, in order to prevent direct conduction and overcurrent damage to the equipment, the dead time ts needs to be set, which is usually set to 1~2us. Since the dead time is short, it is assumed that there is continuous flow during the previous dead time. The analysis of the situation where there is continuous flow during the previous dead time has already included the situation where there is continuous flow during part of the previous dead time. t1 represents a certain moment when the PWM signal of the lower bridge arm is high, and t2 represents the moment when the high level of the PWM signal of the lower bridge arm ends.

[0068] ④ For the H-PWM_L-ON (complementary) modulation mode, the following situations should be discussed: The first case: the duty cycle is small, and the freewheeling ends at time t1. At this time, the equation is satisfied before time t1: e c =u c (u n =0) (6) After time t1 and before time t2, phases A and B satisfy the following equation: At this time, a 、i b is zero, we can get formula (6), the conduction condition of the switch tube is as follows Figure 8 shown.

[0069] When it is in the dead time after t2, the lower bridge arm of phase A is no longer turned on. At this time, only the lower bridge arm switch of phase B is turned on, so the equation is obtained: e c =u c +e b (u n =-e b ) (8) The eb in formula (8) can be obtained by calculating the speed based on the closed-loop given speed or the speed converted from the open-loop duty cycle. The formula in Table 1 is similar.

[0070] The second case: the duty cycle is large, and the current continues during the entire period when the PWM signal of the upper bridge arm of phase A is at a low level. At this time, there is a risk of direct conduction between the upper and lower bridge arms. Equation (7) is still satisfied. The only difference is that ia and ib are not zero at this time. Adding the equations of ua and ub, the expression of formula (6) can be obtained.

[0071] ⑤ Since the modulation mode of H-PWM_L-PWM (complementary) can make the motor rotate forward and reverse, it can be seen from the symmetry that the analysis of the case where the duty cycle D>50% only covers all cases. It is similar to the analysis of the modulation mode of H-PWM_L-ON (complementary), so it will not be repeated.

[0072] ⑥The above analysis does not take into account the influence of parasitic capacitance and capacitor-inductor resonance, and ignores the influence of the switch on and off time.

[0073] (2) The phenomenon of suspended related intermittent current caused by phase inductance is inevitable, but the duration of this current phenomenon is very short. The specific time depends on the parameters and state of the circuit. The interference caused usually appears before the moment when the reverse electromotive force crosses zero during suspension. However, in extreme cases, the interference signal may continue to the moment when the reverse electromotive force crosses zero or after, thereby causing interference. Therefore, analysis is necessary. Considering the suspended related intermittent current, the reverse electromotive force zero-crossing detection method under several PWM modulation modes is analyzed and summarized. Taking the H-PWM_L-PWM modulation mode as an example, the situation where V1 and V6 are turned on and phase C is a suspended phase is analyzed. The conduction schematic diagram is shown as follows. Fig. 9 shown.

[0074] When V1 and V6 are turned on, phase C changes from the on state to the off state, and there is a freewheeling phenomenon. However, this freewheeling phenomenon depends on the time constant of the circuit. It is usually believed that the freewheeling ends before entering the next on stage. Then, when the PWM signal is at a high level, the voltage equation can be obtained as shown in equation (9).

[0075] i a +i b +i c =0 (10) Due to the existence of the C phase continuous flow process, ia+ib≠0, and the equations of the A and B phases in equation (9) cannot be simply added together.

[0076] By adding the three equations in equation (9) and substituting equation (10) into equation (10), we can obtain: e c =U dc -3un (11) Assume that the start time of the freewheeling is t=0, then the expression of the reverse potential of C at this time satisfies the following relationship: e c =at+E (12) Where E is the amplitude of the trapezoidal wave back EMF, and a is the back EMF attenuation coefficient, which can be obtained by the current speed. c The initial value of is I. Using the principle of solving differential equations, the expression of the suspended phase freewheeling current can be obtained as: Usually, since the freewheeling time is very short, it can be assumed that ec maintains the same amplitude E during this period, then: From formula (14), the expression of the continuous flow time can be deduced as:

[0069] Generally speaking, the freewheeling time is very short and can be calculated by formula (15). However, in extreme cases, such as when the winding resistance is small and the inductance is large and under heavy load, the freewheeling time may be longer, and formula (13) may be needed to calculate the freewheeling time. When the freewheeling time is longer, it is necessary to discuss the situation when the PWM signal is low level (off) three-phase freewheeling. At this time, it is only necessary to exchange the voltages of the two phases a and b in formula (9). It is easy to know that formulas (11) to (15) are still valid.

[0077] In order to effectively remove the zero-crossing interference caused by the suspended intermittent current, it is necessary to classify and discuss the moment when the freewheeling interference occurs. Here, the freewheeling diode has a conduction tube voltage drop.

[0078] ① The freewheeling interference continues until the moment when the reverse electromotive force crosses zero. Fig. 9 In the state of intermittent flow of A+B- and suspended phase C, we can get: u C =-U D (16) In the formula, UD is the tube voltage drop of the freewheeling diode when it is forward-conducting. Similarly, when the diode of the upper bridge arm V5 of phase C is freewheeling, it can be obtained that: u C =U dc +U D (17) According to formulas (16) and (17), the commutation flow condition can be obtained by comparing u c >U dc Or u c <0. Therefore, the main part of the zero-crossing interference pulse can be removed by the freewheeling signal. The acquisition of the zero-crossing point of the back electromotive force can refer to the case when the freewheeling of the suspended phase is not considered.

[0079] Finally, a fixed-delay digital filter is used to remove the remaining part of the zero-crossing interference pulse and to achieve fine-tuning of the commutation signal.

[0080] ② The freewheeling interference continues until the back EMF crosses zero or later. At this time, the freewheeling interference can still be removed according to formulas (16) and (17), and fine-tuned by a fixed delay digital filter. The back EMF zero crossing point can be obtained by calculation according to formula (12), and the final commutation signal can be obtained by post-processing.

[0081] The freewheeling time can be calculated according to formula (13) or by sampling and counting the timer according to formulas (16) and (17), and then the time of the back electromotive force corresponding to the electrical angle of 30° is compared to determine the time when the freewheeling interference occurs.

[0082] When considering the dead zone, under the H-PWM_L-PWM (complementary) modulation mode, equations (11) to (15) still hold. Under the modulation mode H-PWM_L-ON (complementary), the differential equations listed have multiple conditions, namely: When the upper bridge arm PWM signal is at a high level, expressions (11) to (17) hold.

[0083] When the upper bridge arm PWM signal is at a low level and phases A and B are in continuous flow, the high level continues for t on When the time jump occurs, expression (9) becomes: At the same time, the value of the current ic at this time can be obtained from expression (13): Then we can solve this problem Current i c The attenuation expression is: Formula (20) shows that the decay rate of the freewheeling current in this stage is slower than that of formula (13). According to different freewheeling conditions, the following equation can be obtained: Fig.10 The current decay diagram is shown in Figure 2. Fig.10 It can be seen that: t off is the conduction duration of the lower bridge arm of the complementary PWM waveform.

[0084] At this time, the continuous flow situation can be divided into two types: ① When the suspended phase continues to flow to the solid arrow or dotted arrow and ends (before the PWM signal jumps to a high level), the continuous flow time is: It should be noted that due to the short freewheeling time, formula (22) ignores the change in the reverse potential of the suspended phase C, that is, it is assumed that ec = E. If the change in the reverse potential is considered, it is a transcendental equation. In most literatures, the expression of current decay is often approximated as a linear decreasing function, and an approximate solution can be obtained.

[0085] ② When the suspended phase continuous current time is long and continues to the next PWM signal cycle, that is, after jumping to a high level, there is: In the formula, i con1 represents the initial value of the next PWM cycle, and the next PWM cycle high level freewheeling process follows the voltage equation of formula (9). The resulting attenuation curve is only different in initial value, and its shape is the same as formula (13).

[0086] In general, the freewheeling current decay process under the H-PWM_L-ON (complementary) modulation mode is a segmented exponential decay. The analysis after the suspension-related intermittent freewheeling ends can refer to the case where the suspension-related intermittent freewheeling is not considered. The analysis of the back-EMF expression under other PWM modulation modes is the same as above and will not be repeated here.

[0087] The above is the theoretical analysis of the improved terminal voltage method proposed by the present invention. Its theoretical innovations are as follows: ① The influence of dead zone is considered when discussing various conditions of freewheeling. The discussion of different freewheeling conditions is relatively comprehensive and summarized in a table.

[0088] ② The situation of continuous current during suspension-related intermittent period was derived in detail, the current attenuation change process was analyzed in detail, and the corresponding zero-crossing point acquisition strategy was proposed, especially when the continuous current time during suspension-related intermittent period was long.

[0089] ③ Conduct a more detailed analysis of the expression of the back electromotive force after the end of the follow-up current.

[0090] ④Analyze the expressions of suspended reverse potential under 8 common PWM modulation methods in different situations.

[0091] In the analysis of the case of continuous current during suspension, the derivation of the expressions of terminal voltages ua, ub, uc, etc. is based on the example of not considering the device conduction voltage drop. If it is considered, the derivation process is the same. The above analysis does not consider the influence of parasitic capacitance and capacitor-inductor resonance, and ignores the influence of the switch on and off time.

[0092] In order to verify the scientific effectiveness of the proposed method, a simulation verification based on Simulink is carried out. Take the PWM chopping when the upper bridge arm is turned on, the complementary PWM chopping of the lower bridge arm, and the high level when turned on, that is, the H-PWM_L-ON (complementary) modulation mode as an example. According to the method proposed in the present invention, the freewheeling signal is filtered out. The specific method is to set the general bridge model in Simulink to IGBT / Diodes, and set the Diodes on-state voltage drop to 0.7V, and remove the freewheeling signal by setting the threshold detection. According to the proposed method to remove the interference of the chopping signal, the specific formula involved is as follows (taking phase A as an example): ①When C+B- is turned on: ②Dead zone continuous flow: e a =u a +0.35 (25) ③When C+ is off and C- is on: e a =u a (26) ④C related break time: e a =u a +e b (27) The analysis when B+C- is on is similar to the above. Formula (27) needs to be changed to: e a =u a +e c (28) By setting a fixed delay, the motor with parameters shown in Table 2 was subjected to no-load and load open-loop tests at a speed of about 2160 r / min (with a load of 2 Nm applied), and no-load start, with a loading time of 0.25 s. Fig.11 The commutation signals and processed back EMF waveforms are shown.

[0093] Table 2 Motor parameters like Fig.11 Shown are the commutation signal obtained by the terminal voltage direct comparison method with 1 / 2 DC bus voltage as the neutral point voltage under the control of the Hall position sensor, the Hall position signal, the back EMF waveform processed by the proposed method, and the commutation signal finally obtained by the proposed method.

[0094] The processed back-EMF waveform can be used to extract the transition edge of the commutation signal, which can be achieved by setting a reasonable threshold and using a linear interpolation method.

[0095] from Fig.11It can be seen that the commutation signal obtained by the terminal voltage direct comparison method has many false jumps, which will cause commutation failure. However, the commutation signal corresponding to the processed back-EMF waveform has greatly reduced zero-crossing false jumps. Finally, the commutation signal obtained by the proposed method is consistent with the Hall signal, which verifies that the proposed method has certain scientificity and feasibility.

[0096] The motor with the parameters shown in Table 2 was tested with no-load and load (with a load of 1Nm) at a speed of about 1525r / min. No-load start, loading time of 0.25s, and the following results were obtained: Fig.11 The commutation signal and processed back EMF waveform are shown.

[0097] from Fig.11 It can be seen that although the commutation signal obtained by the proposed method has a certain error compared with the Hall signal, the fixed delay digital filter can remove this part of the error, which will not be described in detail here.

[0098] So far, the simulation results based on Simulink have verified the scientificity and feasibility of the proposed method.

[0099] The terminal voltage direct comparison method is a simple and low-cost method in the back-electromotive force zero-crossing detection method, but it has detection errors. The present invention proposes a more accurate and improved terminal voltage method based on an in-depth analysis of the expression of the suspended back-electromotive force with 1 / 2 DC bus voltage as the neutral point voltage. The present invention comprehensively derives and analyzes the expression of the suspended back-electromotive force under 8 common PWM modulation modes, covering a variety of conditions during freewheeling, and analyzes the freewheeling process. According to different operating conditions, the corresponding expression is selected to obtain zero-crossing information to weaken the influence of freewheeling and chopping. At the same time, the back-electromotive force expression during freewheeling and chopping and the tube voltage drop and fixed delay of the conducting diode are used to weaken the interference of factors such as PWM chopping and freewheeling during zero-crossing detection. The proposed method is simple, effective and accurate, improves reliability and avoids the problem of delay compensation caused by the filter, and is particularly suitable for electric mechanisms of equipment such as high-voltage circuit breakers.

[0100] The present invention is not limited to the above-mentioned embodiments. No matter any changes are made in the shape or material composition, any structural design provided by the present invention is a variation of the present invention and should be considered to be within the protection scope of the present invention.

Claims

1. A sensorless control method for an electric mechanism, characterized in that: The following steps are involved: S1: Analyze the back EMF zero-crossing detection method under several PWM modulation modes, and obtain the precise expression of the suspended back EMF under various PWM modulation modes under different operating conditions; S2: Obtain the moment when the back electromotive force crosses zero according to the obtained expression, and obtain the commutation signal of the motor by delay; S3: Control the motor to run smoothly according to the power-on sequence; S4: The electric energy storage mechanism enables accurate and rapid opening and closing of the equipment.

2. The sensorless control method of an electric mechanism according to claim 1, characterized in that: The step S1 and the step S2 include the analysis of the situation without considering the suspension-related intermittent flow and the analysis of the situation considering the suspension-related intermittent flow.

3. The sensorless control method of an electric mechanism according to claim 2, characterized in that: In step S1, the analysis of the situation of not considering the suspended intermittent flow includes the following steps: S1.1: Determine whether the upper and lower bridge arms are complementary and turned on. If so, set the dead time and proceed to step S1.

2. If not, proceed to step S1.2; S1.2: According to the high-level on-state, low-level off-state and end-state of the chopped PWM signal in each cycle, the corresponding motor voltage equation is obtained, and the corresponding suspended opposite potential expression is calculated and enters step S2.

4. The sensorless control method of an electric mechanism according to claim 2, characterized in that: In step S1, the analysis of the situation of considering the suspension-related intermittent flow includes the following steps: S1.3: According to the PWM signal of the chopping wave in each cycle being in the high-level conduction state, the low-level shutdown freewheeling state and the low-level freewheeling end state, the corresponding motor voltage equation is obtained, and the expression of the suspended opposite potential is calculated; S1.4: Based on the principle of solving differential equations, the expression of the suspended phase freewheeling current and freewheeling time are obtained; S1.6: The freewheeling time is obtained by comparing whether the suspended phase voltage is greater than the DC bus voltage or less than zero; S1.7: Obtain the corresponding freewheeling end time according to the complementary conduction of the upper and lower bridge arms, and enter step S2.

5. The sensorless control method of an electric mechanism according to claim 4, characterized in that: The step S1.7 comprises the following steps: S1.71: Determine whether the upper and lower bridge arms are complementary and conductive. If so, proceed to step S1.8; if not, proceed to step S1.9; S1.72: Set the dead time, and use the timer to count the duration that the suspended phase voltage is greater than the DC bus voltage or less than zero to obtain the moment when the freewheeling ends, and then go to step S2; S1.73: The moment when the freewheeling ends is obtained by calculating the freewheeling time or by timing the duration of the suspended phase voltage being greater than the DC bus voltage or less than zero through a timer, and then proceeding to step S2.

6. A sensorless control method for an electric mechanism according to claim 1 or 2, characterized in that: In step S2, the following steps are included to consider the case of suspended intermittent flow: S2.1: Compare the back electromotive force time corresponding to the electrical angle of 30° with the freewheeling time to determine the effect of freewheeling on the acquisition of the zero-crossing point; S2.2: Determine whether the continuous flow ends before the back electromotive force crosses zero. If so, proceed to step S2.3; if not, proceed to step S2.4; S2.3: Use reasonable voltage threshold and digital filtering to remove interference, refer to the suspended related continuous flow conditions, select the corresponding back electromotive force expression in combination with the actual situation, or directly obtain the back electromotive force zero crossing point based on the back electromotive force expression, and proceed to step S2.5; S2.4: Obtain the back electromotive force zero crossing point based on the back electromotive force expression; S2.5: Get the accurate back EMF zero-crossing point, delay 30° electrical angle to get the commutation signal, and go to step S3.

7. A sensorless control method for an electric mechanism according to claim 1 or 2, characterized in that: In the step S2, the case of suspended intermittent current is not considered. The corresponding suspended back electromotive force expression is selected according to the parameters and state of the circuit, the moment when the back electromotive force crosses zero is obtained, and the motor commutation is controlled by delaying 30° electrical angle.

8. The sensorless control method of an electric mechanism according to claim 1, characterized in that: The step S2 includes removing the remaining part of the zero-crossing interference pulse and fine-tuning the commutation signal through a fixed-delay digital filter, and obtaining the final commutation signal through post-processing.

9. A sensorless control method for an electric mechanism according to claim 3 or 5, characterized in that: The dead time is set to 1 to 2 us.

10. The sensorless control method of an electric mechanism according to claim 6, characterized in that: The back electromotive force expression is: e=at+E.

Images