Magnetic suspension system and control method and device thereof, storage medium and program product

Abstract

The invention discloses a control method and device of a frequency converter, a magnetic suspension system, a storage medium and a computer program product, the frequency converter is used for supplying power to a motor and a bearing in the magnetic suspension system, the frequency converter is provided with an inverter, and the method comprises the following steps: under the condition that the frequency converter enters an energy feedback stage, obtaining a bus voltage of the frequency converter, obtaining the output current of the inverter, and obtaining the output voltage of the inverter; according to the bus voltage of the frequency converter, the output current of the inverter and the output voltage of the inverter, determining a zero crossing point of the inverter and a dead zone compensation voltage of the inverter; and at the zero crossing point of the inverter, performing dead-zone compensation on the inverter by using the dead-zone compensation voltage of the inverter so as to realize dynamic dead-zone compensation control of the frequency converter at the energy feedback stage. According to the scheme, compensation control is carried out on the dead time of the switching tube in the inverter in the energy feedback stage of the frequency converter, so that the loss of the switching tube is reduced, and the energy feedback efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of magnetic levitation system technology, specifically relating to a control method, device, magnetic levitation system, storage medium, and computer program product for a frequency converter, and particularly to an adaptive dead-zone compensation control method, device, magnetic levitation system, storage medium, and computer program product for the energy feedback stage of a magnetic levitation frequency converter. Background Technology

[0002] In applications such as industrial automation, new energy power generation, and electric vehicles, frequency converters, as core power electronic devices, are widely used to regulate motor speed and achieve efficient energy conversion. During the energy feedback phase of a magnetic levitation frequency converter, the inverter module needs to achieve bidirectional energy flow through the switching of switching devices, with the motor coasting as a generator to provide DC voltage to the bus. However, due to the switching characteristics of the switching devices and the existence of circuit parasitic parameters, the setting of the dead time becomes a key factor affecting system performance. However, the fixed dead time of the switching transistors in the inverter module during the energy feedback phase leads to high losses in the switching transistors within the inverter module.

[0003] The above content is only used to help understand the technical solution of the present invention and does not represent an admission that the above content is prior art. Summary of the Invention

[0004] The purpose of this invention is to provide a control method, device, magnetic levitation system, storage medium, and computer program product for a frequency converter, in order to solve the problem that in the energy feedback stage of a magnetic levitation frequency converter, the inverter module of the frequency converter needs to achieve bidirectional energy flow through the switching of switching devices, but the fixed dead time of the switching transistors in the inverter module leads to high losses of the switching transistors. The invention achieves the effect of reducing switching transistor losses and improving energy feedback efficiency by compensating for and controlling the dead time of the switching transistors in the inverter during the energy feedback stage of the frequency converter.

[0005] This invention provides a control method for a frequency converter, which supplies power to a motor and bearings in a magnetic levitation system. The frequency converter includes an inverter. The control method includes: when the frequency converter enters the energy feedback phase, acquiring the bus voltage of the frequency converter, acquiring the output current of the inverter, and acquiring the output voltage of the inverter; determining the zero-crossing point and the dead-zone compensation voltage of the inverter based on the bus voltage, the output current, and the output voltage of the inverter; and performing dead-zone compensation on the inverter at the zero-crossing point using the dead-zone compensation voltage to achieve dynamic dead-zone compensation control of the frequency converter during the energy feedback phase.

[0006] In some implementations, determining the zero-crossing point and dead-zone compensation voltage of the inverter based on the inverter's bus voltage, the inverter's output current, and the inverter's output voltage includes: compensating the modulation voltage of the inverter's SVPWM control module based on the phase current in the inverter's output current and the inverter's bus voltage; then, determining the inverter's zero-crossing point and dead-zone compensation voltage based on the inverter's output voltage.

[0007] In some implementations, the modulation voltage of the SVPWM control module of the inverter is compensated based on the phase current in the output current of the inverter and the bus voltage of the inverter. This includes: determining the compensation voltage per phase of the inverter based on the phase current in the output current of the inverter and the bus voltage of the inverter; calculating the compensation voltage per phase of the inverter to obtain the calculated compensation voltage per phase of the inverter; and superimposing the calculated compensation voltage per phase of the inverter onto the waveform of the SVPWM modulation output of the inverter to compensate the modulation voltage of the SVPWM control module of the inverter.

[0008] In some implementations, determining the compensation voltage per phase of the inverter based on the phase current in the inverter's output current and the bus voltage of the inverter includes: calculating the compensation voltage per phase of the inverter according to the following formula based on the phase current in the inverter's output current and the bus voltage of the inverter:

[0009] ;

[0010] Among them, U abu T represents the A-phase compensation voltage of the inverter, determined based on the A-phase current in the inverter's output current. d T represents the dead time of the inverter. s U represents the carrier period of the inverter. dc i represents the bus voltage of the frequency converter. a sgn(i) represents the A-phase current in the output current of the inverter. a ) represents a sign function;

[0011] And / or, the compensation voltage of each phase of the inverter is calculated to obtain the calculated compensation voltage of each phase of the inverter, including:

[0012] U mbu =U abu •K1•U △ / U dc ;

[0013] Among them, U mbu U represents the A-phase compensation voltage of the inverter. abu This represents the A-phase compensation voltage of the inverter, determined based on the A-phase current in the inverter's output current. K1 represents a preset calculation coefficient, and U... △ U represents the triangular carrier amplitude of the inverter. dc This indicates the bus voltage of the frequency converter.

[0014] In some implementations, determining the zero-crossing point and dead-zone compensation voltage of the inverter based on the output voltage of the inverter includes: determining the zero-crossing point of the inverter based on the output voltage of the inverter; and determining the dead-zone compensation voltage of the inverter at the zero-crossing point of the inverter.

[0015] In some embodiments, determining the zero-crossing point of the inverter based on its output voltage includes: determining the maximum and minimum values ​​of the inverter's output voltage obtained a set number of consecutive times, denoted as the inverter's maximum output voltage and minimum output voltage; if the product of the inverter's maximum output voltage and minimum output voltage is greater than 0, then the time period during which the inverter's output voltage is obtained a set number of consecutive times is determined as the inverter's zero-crossing point; wherein, if the inverter's maximum output voltage is obtained before the inverter's minimum output voltage, then the inverter's zero-crossing point is determined to be a zero-crossing point transitioning from the positive half-cycle to the negative half-cycle; if the inverter's minimum output voltage is obtained before the inverter's maximum output voltage, then the inverter's zero-crossing point is determined to be a zero-crossing point transitioning from the negative half-cycle to the positive half-cycle.

[0016] And / or, at the zero-crossing point of the inverter, determine the dead-zone compensation voltage of the inverter, including: determining the difference between the ideal output voltage of the inverter and the output voltage of the inverter obtained at the zero-crossing point of the inverter, and recording it as the output voltage difference of the inverter; multiplying the ratio of the output voltage difference of the inverter to the ideal output voltage of the inverter by the product of the amplitude of the triangular carrier wave of the inverter, and determining it as the dead-zone compensation voltage of the inverter; and then: superimposing the dead-zone compensation voltage of the inverter onto the waveform of the SVPWM modulation output of the inverter to perform dead-zone compensation on the inverter, so as to realize dynamic dead-zone compensation control of the inverter in the energy feedback stage.

[0017] In conjunction with the above method, another aspect of the present invention provides a control device for a frequency converter, comprising: an acquisition unit configured to acquire the bus voltage of the frequency converter, the output current of the inverter, and the output voltage of the inverter when the frequency converter enters the energy feedback phase; a control unit configured to determine the zero-crossing point of the inverter and the dead-zone compensation voltage of the inverter based on the bus voltage of the frequency converter, the output current of the inverter, and the output voltage of the inverter; the control unit is further configured to perform dead-zone compensation on the inverter at the zero-crossing point using the dead-zone compensation voltage of the inverter, so as to realize dynamic dead-zone compensation control of the frequency converter in the energy feedback phase.

[0018] In conjunction with the above-mentioned device, the present invention further provides a magnetic levitation system, including: the control device for the frequency converter described above.

[0019] In conjunction with the above method, the present invention further provides a storage medium comprising a stored program, wherein, when the program is executed, the device containing the storage medium is controlled to perform the steps of the frequency converter control method described above.

[0020] In conjunction with the above method, the present invention further provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the frequency converter control method described above.

[0021] Therefore, the solution of this invention is for a frequency converter (such as a magnetic levitation frequency converter). The frequency converter has a rectifier and an inverter. The rectifier outputs a bus voltage to power the bearing power supply, and the inverter outputs an AC voltage to power the motor. When the frequency converter enters the energy feedback stage, the dead time of the switching transistors in the inverter is compensated and controlled according to the output current, output voltage, and bus voltage of the inverter. Thus, by compensating and controlling the dead time of the switching transistors in the inverter during the energy feedback stage of the frequency converter, the losses of the switching transistors are reduced and the energy feedback efficiency is improved.

[0022] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating an embodiment of the inverter control method of the present invention;

[0025] Figure 2This is a flowchart illustrating an embodiment of the method of the present invention for determining the dead-zone compensation voltage and the dead-zone compensation time of the inverter;

[0026] Figure 3 This is a flowchart illustrating an embodiment of the method of the present invention for compensating the modulation voltage of the SVPWM control module of the frequency converter;

[0027] Figure 4 This is a flowchart illustrating an embodiment of the method of the present invention for determining the dead-time compensation of the inverter;

[0028] Figure 5 In the method of the present invention

[0029] A flowchart of one embodiment;

[0030] Figure 6 This is a flowchart illustrating an embodiment of the method of the present invention for determining the dead-time compensation time of the inverter at the zero-crossing point of the inverter.

[0031] Figure 7 This is a schematic diagram of the structure of a control device for the frequency converter of the present invention;

[0032] Figure 8 This is a schematic diagram of a magnetic levitation frequency converter system.

[0033] Figure 9 This is a schematic diagram of the energy feedback phase of a magnetic levitation system during power outages.

[0034] Figure 10 This is a block diagram of the energy feedback control for a permanent magnet synchronous motor with dead-zone compensation.

[0035] Figure 11 This is a flowchart illustrating the process of determining the zero-crossing point.

[0036] Referring to the accompanying drawings, the reference numerals in the embodiments of the present invention are as follows:

[0037] 102 - Acquisition unit; 104 - Control unit. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] Considering that during the energy feedback phase of a magnetic levitation frequency converter, the inverter module needs to achieve bidirectional energy flow through the switching of switching devices, but the fixed dead time of the switching transistors in the inverter module leads to high losses in the switching transistors. Specifically, under ideal conditions, the inverter module has low losses when driven without dead time. However, in actual applications, the absence of dead time can cause shoot-through in the switching transistors of the upper and lower bridge arms of the inverter module, resulting in a short circuit between the upper and lower bridge arms. To avoid shoot-through, a dead time is added. The addition of dead time increases the losses of the switching transistors in the inverter module. In other words, the fixed dead time of the inverter module during the energy feedback phase of the magnetic levitation frequency converter leads to high losses in the inverter module.

[0040] Furthermore, due to the fixed dead time of the inverter module, there will be significant current harmonics and waveform distortion, thus affecting the energy feedback efficiency of the magnetic levitation inverter. In related solutions, the fixed dead time affects energy feedback, requiring the inverter module to perform more switching operations to compensate for the impact, thereby reducing the lifespan of the switching devices in the inverter module.

[0041] Therefore, the present invention proposes a control method for a frequency converter, specifically an adaptive dead-time compensation control method for the energy feedback stage of a magnetic levitation frequency converter. In the energy feedback stage, by precisely controlling the dead time of the switching transistors, the losses of the switching transistors in the inverter module during the energy feedback stage of the magnetic levitation frequency converter are reduced.

[0042] According to embodiments of the present invention, a control method for a frequency converter is provided, such as... Figure 1 The diagram shows a flowchart of an embodiment of the method of the present invention. The frequency converter is used to supply power to the motor and bearings in the magnetic levitation system. The frequency converter has an inverter, and the inverter has a switching transistor (such as an IGBT). In the solution of the present invention, as... Figure 1 As shown, the control method of the frequency converter includes steps S110 to S130.

[0043] In step S110, if a power outage occurs during the operation of the frequency converter, the motor coasts and the frequency converter enters the energy feedback stage; when the frequency converter enters the energy feedback stage, the bus voltage of the frequency converter, the output current of the inverter, and the output voltage of the inverter are obtained.

[0044] In step S120, the zero-crossing point and dead-zone compensation voltage of the inverter are determined based on the bus voltage of the frequency converter, the output current of the inverter, and the output voltage of the inverter.

[0045] At step S130, at the zero-crossing point of the inverter, the inverter is dead-zone compensated using the dead-zone compensation voltage of the inverter to achieve dynamic dead-zone compensation control of the inverter during the energy feedback stage.

[0046] Figure 8 This is a schematic diagram of a magnetic levitation frequency converter system. Figure 8 The diagram shows a frequency converter model. The rectifier side consists of an AC input power supply and IGBT switching transistors, while the inverter side consists of IGBT switching transistors and a load forming the inverter circuit. The freewheeling diodes of the IGBT switching transistors on the rectifier side are diodes D1, D2, D3, D4, D5, and D6. The IGBT switching transistors on the rectifier side are transistors Q1, Q2, Q3, Q4, Q5, and Q6. The DC bus voltage output from the rectifier side supplies power to the bearing power supply.

[0047] See Figure 8 In the example shown, when the inverter experiences an abnormal power outage, the input power supply terminal at the rectifier side is disconnected, leaving only the inverter and motor M operating. The back electromotive force generated by the motor's coasting motion restores the bus voltage to the given value. During coasting, the motor essentially transforms from a motor into a generator, maintaining the bus voltage through generator principles. Since the bearing is in a suspended state during a sudden power outage, and its power supply is drawn from the inverter bus, a sudden drop in bus voltage could lead to insufficient voltage for the bearing to remain suspended, causing the bearing to strike and resulting in irreversible damage to both the bearing and the shaft. Therefore, during a sudden power outage, the inverter utilizes the back electromotive force generated by the motor's coasting motion, and through a control algorithm, controls the IGBTs on the inverter side to restore the bus voltage to the given value. Furthermore, during coasting, the bus voltage is maintained at a level sufficient to supply the bearing power supply for normal operation, ensuring the safe operation of the equipment.

[0048] Figure 9 This is a schematic diagram of the energy feedback phase of a magnetic levitation system during power outages. Figure 9 The diagram shown is a schematic of energy feedback. Figure 9 This demonstrates the flow of the voltage and current dual closed-loop algorithm. For example... Figure 9 As shown, the power grid supplies power to the motor through the rectifier and inverter sides. The DC bus voltage output from the rectifier side supplies power to the bearing power supply. Power outage detection is performed between the power grid and the rectifier side, and the detection result is transmitted to the bearing power supply. The bearing power supply supplies power to the bearing control system, which in turn controls the bearing operation. When power is lost at high speed, the motor control system performs voltage and current dual closed-loop space vector pulse width modulation (SVPWM) rectification and energy feedback to ensure the energy supply for the magnetic levitation bearing control.

[0049] Figure 10This is a block diagram of energy feedback control for a permanent magnet synchronous motor using dead-zone compensation. Figure 10 The diagram shown is a control block diagram for the power-off energy feedback stage of a permanent magnet synchronous motor using complementary master high-level dead-time compensation. Figure 10 Dynamic dead time compensation has been added. For example... Figure 10 As shown, the control employs a dual closed-loop control system consisting of a current loop and a speed loop (and...). Figure 9 (Consistent), the decoupling of the d-axis and q-axis currents is achieved through coordinate transformation, and the system has excellent static and dynamic response characteristics.

[0050] See Figure 10 In the example shown, the given value U of the bus voltage dc * With actual bus voltage U dc Compared to obtaining the DC current setpoint (i.e., the q-axis setpoint current) via a PI controller, this is achieved through a PI controller. q * The output current i of the three-phase inverter a i b i c The α-axis current i is obtained through Clarke transformation. α β-axis current i β Then, after Park transformation, the d-axis current i is obtained. d q-axis current i q q-axis given current i q * With q-axis current i q The comparison is then processed by a PI controller to obtain u. q d-axis given current i d * With q-axis current i d The d-axis voltage u obtained by the PI controller is compared. d d-axis voltage u d With q-axis voltage u q The α-axis voltage u is obtained through Park's inverse transform. α β-axis voltage u β Then, through the SVPWM control module, the complementary master high-level dead-time compensation module, and the zero-crossing point judgment module, the switching time of each sector is confirmed, and the conduction time of each bridge arm switch is obtained. The complementary master high-level dead-time compensation module calculates the dead-time compensation voltage based on the difference between the output voltage under ideal conditions and after adding the dead time, and feeds it back to the SVPWM control module. Coordinate transformation yields the d-axis current i. d q-axis current i q d-axis given current i d * q-axis given current i q * These are reference values, manually assigned. Figure 10In the example shown, a dynamic dead time calculation algorithm is added to improve energy feedback efficiency.

[0051] The present invention proposes an adaptive dead-time compensation control strategy for the energy feedback stage of a magnetic levitation frequency converter. By precisely controlling the dead time of the switching transistors during the energy feedback stage, the losses of the switching transistors in the inverter module during the energy feedback stage of the magnetic levitation frequency converter can be reduced, the energy feedback efficiency can be improved, the life of the switching devices can be extended, and the power quality can be improved.

[0052] In the solution of this invention, the core function of dead-time compensation is to solve the performance defects caused by fixed dead time by dynamically adjusting the dead time. The complementary main high-level dead-time compensation method is a control technology used to optimize the control of power switching devices. It combines complementary signal control and dynamic adjustment of dead time to improve the efficiency, stability and reliability of the circuit, thereby reducing current harmonics, reducing waveform distortion, reducing switching losses and device stress, enhancing system stability and dynamic response, reducing electromagnetic interference, improving energy feedback efficiency, thereby extending device life, improving electromagnetic compatibility and improving power quality.

[0053] In some implementations, the specific process of determining the zero-crossing point and dead-zone compensation voltage of the inverter based on the bus voltage of the frequency converter, the output current of the inverter, and the output voltage of the inverter in step S120 is illustrated in the following exemplary description.

[0054] The following is combined Figure 2 The schematic diagram shows an embodiment of the method of the present invention for determining the dead-zone compensation voltage and the dead-zone compensation time of the inverter. It further illustrates the specific process of determining the dead-zone compensation voltage and the dead-zone compensation time of the inverter in step S120, including steps S210 to S220.

[0055] Step S210: Compensate the modulation voltage of the SVPWM control module of the inverter based on the phase current in the output current of the inverter and the bus voltage of the inverter.

[0056] Step S220: Afterwards, the zero-crossing point and dead-zone compensation voltage of the inverter are determined based on the output voltage of the inverter.

[0057] In the present invention, a dead-time compensation control strategy is proposed for magnetic levitation cooling frequency converters. During the energy feedback stage, the performance defects caused by fixed dead time are solved by precisely controlling the dead time of the switching transistors. This reduces current harmonics, waveform distortion, switching losses and device stress, enhances system stability and dynamic response, reduces electromagnetic interference, and improves energy feedback efficiency, thereby extending device life, improving electromagnetic compatibility, and enhancing power quality.

[0058] In some embodiments, the specific process of compensating the modulation voltage of the SVPWM control module of the inverter based on the phase current in the output current of the inverter and the bus voltage of the inverter in step S210 is described in the following exemplary description.

[0059] The following is combined Figure 3 The diagram shows a flowchart of an embodiment of the method of the present invention for compensating the modulation voltage of the SVPWM control module of the frequency converter. The specific process of compensating the modulation voltage of the SVPWM control module of the frequency converter in step S210 is further explained, including steps S310 to S330.

[0060] Step S310: Determine the compensation voltage for each phase of the inverter based on the current of each phase in the output current of the inverter and the bus voltage of the frequency converter. The compensation voltage for each phase of the inverter is, for example, the compensation voltage U of phase A of the inverter. abu .

[0061] Step S320: The compensation voltage for each phase of the inverter is calculated to obtain the calculated compensation voltage for each phase of the inverter. The calculated compensation voltage for each phase of the inverter is, for example, the calculated compensation voltage U for phase A of the inverter. mbu .

[0062] Step S330: The calculated compensation voltage of each phase of the inverter is superimposed on the waveform of the SVPWM modulation output of the inverter to compensate the modulation voltage of the SVPWM control module of the frequency converter.

[0063] In the scheme of this invention, based on the complementary main high-level dead-time compensation control strategy, the dead time is precisely controlled by the difference between the inverter output voltage under ideal conditions and the inverter output voltage after the dead time is added.

[0064] In some implementations, step S310, determining the compensation voltage for each phase of the inverter based on the current in each phase of the inverter's output current and the bus voltage of the frequency converter, includes:

[0065] Based on the current of each phase in the output current of the inverter and the bus voltage of the frequency converter, the compensation voltage of each phase of the inverter is calculated according to the following formula:

[0066] ;

[0067] Among them, U abu T represents the A-phase compensation voltage of the inverter, determined based on the A-phase current in the inverter's output current. d T represents the dead time of the inverter. s U represents the carrier period of the inverter. dc i represents the bus voltage of the frequency converter. a sgn(i) represents the A-phase current in the output current of the inverter. a ) represents a symbolic function.

[0068] And / or, in step S320, the compensation voltage of each phase of the inverter is calculated to obtain the calculated compensation voltage of each phase of the inverter, including:

[0069] U mbu =U abu •K1•U △ / U dc ;

[0070] Among them, U mbu U represents the A-phase compensation voltage of the inverter. abu This represents the A-phase compensation voltage of the inverter, determined based on the A-phase current in the inverter's output current. K1 represents a preset calculation coefficient, and U... △ U represents the triangular carrier amplitude of the inverter. dc This represents the bus voltage of the frequency converter. Preferably, K1 is 2, which yields the formula (2).

[0071] Figure 11 This is a flowchart illustrating the zero-crossing determination process. Figure 11 The diagram shown is a flowchart for determining zero crossing points. Figure 11 As shown, the zero-crossing point determination process includes:

[0072] Step 1: Enter the energy feedback phase, then proceed to Step 2.

[0073] When the magnetic levitation frequency converter experiences a sudden power outage Figure 8 When the input voltage at the rectifier front end is 0, the energy feedback stage begins. At this time, the motor is still coasting. The motor and the H-bridge (i.e., the three-phase full-bridge inverter on the inverter side) form a generator. By controlling the switching transistors, the generated electricity is input to the bus, providing sufficient voltage for the magnetic levitation bearing power supply, thus keeping the magnetic levitation bearing levitated until the coasting ends.

[0074] Step 2: Complementary master high-level dead zone compensation, then proceed to step 3.

[0075] This method detects the polarity of the inverter's three-phase output current, calculates the error square wave voltage, and then superimposes it onto the modulation wave of the SVPWM output after appropriate conversion. This square wave signal causes the inverter to generate a compensation voltage that is in phase with the current. The algorithm contains internal calculation coefficients such as per-unit values, which need to be converted before being superimposed on the modulation wave. Essentially, this method averages the error voltage over each switching cycle.

[0076] The compensation voltage for phase A can be expressed as:

[0077] (1).

[0078] In the above formula, T d For dead time, T s For the carrier period, U dc For DC bus voltage, sgn(i a ) is a symbolic function, when (i a When >0), sgn(i a )=1; when (i a When <0), sgn(i a = -1. Definition: Current flowing out of the inverter bridge arm is positive, and current flowing into the inverter bridge arm is negative. a This represents the current in phase A. Phases B and C use the same compensation value.

[0079] When the compensation voltage is superimposed on the waveform of the SVPWM modulation output, corresponding calculations are required. According to the modulation principle of SVPWM, the modulation voltage and the compensation voltage have the following relationship:

[0080] (2).

[0081] In the above formula, U m U is the modulation voltage (i.e., the modulation amplitude). △ U is the amplitude of the triangular carrier wave. dc U is the DC bus voltage. abu This is the compensation voltage for phase A.

[0082] When the compensation voltage U of phase A abu When superimposed on the waveform of the SVPWM modulation output, reverse calculation is required, and the calculated compensation voltage U mbu The reduced compensation voltage U is calculated by combining formulas (1) and (2). mbu As shown in the following formula:

[0083] (3).

[0084] Furthermore, unlike traditional dead-time compensation where the conduction times of the upper and lower bridge arms are completely opposite (i.e., the lower (upper) bridge arm is turned on when the upper (lower) bridge arm is turned on), the conduction times of the upper and lower bridge arms differ by 2T in complementary master high-level dead-time compensation. dead Therefore, when the upper bridge arm modulated voltage compensation U abu At the same time, the lower bridge arm also compensates for U. abu This improves energy feedback efficiency and reduces switching losses. dead Indicates dead time.

[0085] In the present invention, a dead-time compensation control strategy is proposed for magnetic levitation cooling inverters, which precisely controls the dead time of the switching transistors during the energy feedback stage.

[0086] In some implementations, the specific process of determining the zero-crossing point and dead-zone compensation voltage of the inverter based on the output voltage of the inverter in step S220 is illustrated in the following exemplary description.

[0087] The following is combined Figure 4 The flowchart shown is a schematic diagram of an embodiment of the method of the present invention for determining the dead time compensation time of the inverter. The specific process of determining the dead time compensation time of the inverter in step S220 is further explained, including steps S410 to S420.

[0088] Step S410: Determine the zero-crossing point of the inverter based on the output voltage of the inverter.

[0089] Step S420: Determine the dead-zone compensation voltage of the inverter at the zero-crossing point of the inverter.

[0090] In the solution of this invention, the dead time is dynamically adjusted, thereby reducing current harmonics, reducing waveform distortion, reducing switching losses and device stress, enhancing system stability and dynamic response, reducing electromagnetic interference, and improving energy feedback efficiency, thereby extending device life, improving electromagnetic compatibility, and improving power quality.

[0091] In some implementations, the specific process of determining the zero-crossing point of the inverter based on the output voltage of the inverter in step S410 is described in the following exemplary description.

[0092] The following is combined Figure 5 The flowchart shown is a schematic diagram of an embodiment of the method of the present invention for determining the zero-crossing point of the inverter. The specific process of determining the zero-crossing point of the inverter in step S410 is further explained, including steps S510 to S520.

[0093] Step S510: Determine the maximum and minimum values ​​of the inverter's output voltage obtained a set number of consecutive times, and record them as the inverter's maximum output voltage and minimum output voltage.

[0094] Step S520: If it is determined that the product of the inverter's maximum output voltage and the inverter's minimum output voltage is greater than 0, then the time period during which the inverter's output voltage is obtained for a set number of consecutive times is determined as the inverter's zero-crossing point.

[0095] Wherein, if the maximum output voltage of the inverter is obtained before the minimum output voltage of the inverter, then the zero-crossing point of the inverter is determined to be the zero-crossing point of the transition from the positive half-cycle to the negative half-cycle; if the minimum output voltage of the inverter is obtained before the maximum output voltage of the inverter, then the zero-crossing point of the inverter is determined to be the zero-crossing point of the transition from the negative half-cycle to the positive half-cycle.

[0096] And / or, in step S420, the specific process of determining the dead-zone compensation voltage of the inverter at the zero-crossing point of the inverter is described in the following exemplary description.

[0097] The following is combined Figure 6 The schematic diagram shows an embodiment of the method of the present invention in which the dead time compensation time of the inverter is determined at the zero-crossing point of the inverter. The specific process of determining the dead time compensation time of the inverter at the zero-crossing point in step S420 is further explained, including steps S610 to S620.

[0098] Step S610: Determine the difference between the ideal output voltage of the inverter and the output voltage of the inverter obtained at the zero-crossing point of the inverter, and record it as the output voltage difference of the inverter.

[0099] Step S620: The ratio of the output voltage difference of the inverter to the ideal output voltage of the inverter, and the product of the amplitude of the triangular carrier wave of the inverter, are determined as the dead-zone compensation voltage of the inverter; the dead-zone compensation voltage of the inverter is then superimposed on the waveform of the SVPWM modulation output of the inverter to perform dead-zone compensation on the inverter, so as to realize dynamic dead-zone compensation control of the inverter in the energy feedback stage.

[0100] like Figure 11 As shown, the zero-crossing point determination process also includes:

[0101] Step 3: Determine the zero-crossing point, then proceed to step 4.

[0102] The inverter's output voltage was continuously sampled 5 times and recorded as U in chronological order. out1 U out2 Uout3 U out4 U out5 The maximum output voltage U is obtained by comparison. outmax With minimum output voltage U outmin Determine the maximum output voltage U outmax With minimum output voltage U outmin The product U outmax ×U outmin If the product is greater than 0, then the point is not at a zero-crossing point; if the product is less than 0, then the point is at a zero-crossing point.

[0103] When it is determined that it is at a zero-crossing point, the maximum output voltage U is determined. outmax With minimum output voltage U outmin Which one is acquired first in time, if the maximum output voltage U outmax If the data is collected first, then it is at the zero-crossing point during the transition from the positive half-cycle to the negative half-cycle; conversely, if the minimum output voltage U is collected later... outmin The data collected earlier is at the zero-crossing point during the transition from the negative half-cycle to the positive half-cycle, providing the necessary calculation parameters for the control algorithm.

[0104] Step 4: Calculate the difference between ideal conditions and the output voltage under dead zone.

[0105] Sampled real-time output voltage U out Simulate the output voltage U without adding a dead time. out * The output voltage under ideal conditions (i.e., the output voltage U without dead time) out * ) and the output voltage when the dead zone is added (i.e., the real-time output voltage U) out The difference ΔU out After calculation, the compensation voltage U is obtained. bc This voltage difference is superimposed on the modulation wave of the SVPWM output to improve energy feedback efficiency and reduce switching losses. The formula for the voltage difference is shown below:

[0106] (4).

[0107] Among them, the compensation voltage U bc As shown below:

[0108] (5).

[0109] According to the compensation voltage U bc After compensation is applied to the modulation wave of the SVPWM output, the SVPWM control module adjusts the compensation voltage U. bcThe dynamic dead zone compensation time is calculated, which is the turn-on time of the switching transistors in the inverter module. The inverter module is then controlled to operate based on the calculated turn-on time of the switching transistors in the inverter module.

[0110] In the scheme of this invention, a complementary main high-level dead-time compensation control strategy is adopted. Based on the complementary main high-level dead-time compensation control strategy, the dead time is precisely controlled by the difference between the inverter output voltage under ideal conditions and the inverter output voltage after adding the dead time. Voltage feedforward compensation is performed in the positive and negative half-cycles of the modulation voltage respectively. In addition, zero-crossing point judgment is added to solve the problem of poor compensation effect at the current zero-crossing point of conventional dead-time compensation methods, thereby optimizing the dead-time compensation efficiency, improving the dead-time compensation accuracy, reducing the impact of the dead time on the circuit, and improving the stability and reliability of the circuit.

[0111] The present invention, based on the energy feedback control method, incorporates dynamic dead-time compensation to improve energy feedback efficiency. The present invention dynamically manages the dead time of the switching transistors, and by precisely controlling the dead time, it solves the performance defects caused by a fixed dead time, reducing current harmonics and waveform distortion. In the present invention, intelligent control of the dead time improves the accuracy of dead-time compensation, reduces the impact of the dead time on the circuit, and enhances circuit stability and reliability.

[0112] The solution of this invention can be applied to the control system of a magnetic levitation frequency converter employing dead-zone compensation. The solution incorporates zero-crossing detection, adaptive compensation, and dead-zone compensation during the energy feedback phase. This results in low computational complexity, a simple control method, and high fault tolerance. Adaptive compensation allows for real-time adjustment of dead-zone control, improving efficiency and stability. The addition of zero-crossing detection avoids the problem of poor dead-zone compensation near the zero-crossing point. Dead-zone compensation during the energy feedback phase improves energy utilization and reduces switching device losses.

[0113] The technical solution of this embodiment addresses a frequency converter (such as a magnetic levitation frequency converter), which has a rectifier and an inverter. The rectifier outputs a bus voltage to power the bearing, and the inverter outputs an AC voltage to power the motor. When the frequency converter enters the energy feedback stage, the dead time of the switching transistors in the inverter is compensated based on the inverter's output current, output voltage, and bus voltage. Thus, by compensating for the dead time of the switching transistors in the inverter during the energy feedback stage of the frequency converter, the losses of the switching transistors are reduced, and the energy feedback efficiency is improved.

[0114] According to an embodiment of the present invention, a control device for a frequency converter corresponding to a control method for a frequency converter is also provided. See also Figure 7The diagram shows a structural schematic of an embodiment of the device of the present invention. The control device of the frequency converter may include: an acquisition unit 102 and a control unit 104.

[0115] The acquisition unit 102 is configured to, in the event of a power outage during the operation of the frequency converter, cause the motor to coast and the frequency converter to enter the energy feedback phase; and, while the frequency converter is in the energy feedback phase, acquire the bus voltage of the frequency converter, acquire the output current of the inverter, and acquire the output voltage of the inverter. The specific functions and processing of this acquisition unit 102 are described in step S110.

[0116] The control unit 104 is configured to determine the zero-crossing point and dead-zone compensation voltage of the inverter based on the bus voltage of the frequency converter, the output current of the inverter, and the output voltage of the inverter. The specific functions and processing of the control unit 104 are described in step S120.

[0117] The control unit is further configured to perform dead-zone compensation on the inverter at the zero-crossing point using the inverter's dead-zone compensation voltage, thereby achieving dynamic dead-zone compensation control of the inverter during the energy feedback phase. The specific functions and processing of this control unit 104 are further described in step S130.

[0118] In the solution of this invention, an adaptive dead-time compensation control strategy is adopted for the energy feedback stage of the magnetic levitation frequency converter. By precisely controlling the dead time of the switching transistors during the energy feedback stage, the losses of the switching transistors in the inverter module during the energy feedback stage of the magnetic levitation frequency converter can be reduced, the energy feedback efficiency can be improved, the life of the switching devices can be extended, and the power quality can be improved.

[0119] Since the processing and functions implemented by the device in this embodiment are basically the same as the embodiments, principles and examples of the aforementioned methods, any details not covered in the description of this embodiment can be found in the relevant descriptions in the aforementioned embodiments, and will not be repeated here.

[0120] According to an embodiment of the present invention, a magnetic levitation system corresponding to a control device for a frequency converter is also provided. This magnetic levitation system may include the control device for the frequency converter described above.

[0121] Since the processing and functions implemented by the magnetic levitation system in this embodiment are basically the same as the embodiments, principles and examples of the aforementioned devices, any details not covered in this embodiment can be found in the relevant descriptions in the aforementioned embodiments, and will not be repeated here.

[0122] According to an embodiment of the present invention, a computer program product corresponding to the control method for a frequency converter is also provided, comprising a computer program that, when executed by a processor, implements the steps of the control method for the frequency converter described above.

[0123] Since the processing and functions implemented by the product in this embodiment are basically the same as the embodiments, principles and examples of the aforementioned methods, any details not covered in the description of this embodiment can be found in the relevant descriptions in the aforementioned embodiments, and will not be repeated here.

[0124] According to an embodiment of the present invention, a storage medium corresponding to a control method for a frequency converter is also provided, the storage medium including a stored program, wherein, when the program is executed, the device where the storage medium is located executes the steps of the control method for the frequency converter described above.

[0125] Since the processing and functions implemented by the storage medium in this embodiment are basically the same as the embodiments, principles and examples of the aforementioned methods, any details not covered in this embodiment can be found in the relevant descriptions in the aforementioned embodiments, and will not be repeated here.

[0126] In summary, it is readily understood by those skilled in the art that, without conflict, the aforementioned advantageous methods can be freely combined and superimposed.

[0127] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A control method for a frequency converter, characterized in that, The frequency converter is used to supply power to the motor and bearings in the magnetic levitation system, and the frequency converter has an inverter; the control method of the frequency converter includes: When the frequency converter enters the energy feedback stage, the bus voltage of the frequency converter, the output current of the inverter, and the output voltage of the inverter are obtained. Based on the bus voltage of the inverter, the output current of the inverter, and the output voltage of the inverter, determine the zero-crossing point and the dead-zone compensation voltage of the inverter; At the zero-crossing point of the inverter, the dead-zone compensation voltage of the inverter is used to perform dead-zone compensation on the inverter, so as to realize dynamic dead-zone compensation control of the inverter in the energy feedback stage.

2. The control method for the frequency converter according to claim 1, characterized in that, Based on the inverter's bus voltage, the inverter's output current, and the inverter's output voltage, determine the inverter's zero-crossing point and dead-zone compensation voltage, including: The modulation voltage of the SVPWM control module of the inverter is compensated based on the phase current in the output current of the inverter and the bus voltage of the inverter. Then, based on the output voltage of the inverter, the zero-crossing point of the inverter and the dead-zone compensation voltage of the inverter are determined.

3. The control method for the frequency converter according to claim 2, characterized in that, Based on the phase current in the inverter's output current and the bus voltage of the inverter, the modulation voltage of the inverter's SVPWM control module is compensated, including: The compensation voltage for each phase of the inverter is determined based on the current of each phase in the output current of the inverter and the bus voltage of the frequency converter. The compensation voltage of each phase of the inverter is calculated to obtain the calculated compensation voltage of each phase of the inverter; The calculated compensation voltage for each phase of the inverter is superimposed onto the waveform of the inverter's SVPWM modulation output to compensate the modulation voltage of the inverter's SVPWM control module.

4. The control method for the frequency converter according to claim 3, characterized in that, in, The compensation voltage for each phase of the inverter is determined based on the output current of the inverter and the bus voltage of the frequency converter, including: Based on the current of each phase in the output current of the inverter and the bus voltage of the frequency converter, the compensation voltage of each phase of the inverter is calculated according to the following formula: ； Among them, U abu T represents the A-phase compensation voltage of the inverter, determined based on the A-phase current in the inverter's output current. d T represents the dead time of the inverter. s U represents the carrier period of the inverter. dc i represents the bus voltage of the frequency converter. a sgn(i) represents the A-phase current in the output current of the inverter. a ) represents a sign function; And / or, The compensation voltage of each phase of the inverter is calculated to obtain the calculated compensation voltage of each phase of the inverter, including: IN mbu =U abu •K1•U △ / IN dc ; Among them, U mbu U represents the A-phase compensation voltage of the inverter. abu This represents the A-phase compensation voltage of the inverter, determined based on the A-phase current in the inverter's output current. K1 represents a preset calculation coefficient, and U... △ U represents the triangular carrier amplitude of the inverter. dc This indicates the bus voltage of the frequency converter.

5. The control method for the frequency converter according to any one of claims 2 to 4, characterized in that, Determining the zero-crossing point and dead-zone compensation voltage of the inverter based on its output voltage includes: Determine the zero-crossing point of the inverter based on its output voltage; At the zero-crossing point of the inverter, the dead-zone compensation voltage of the inverter is determined.

6. The control method for a frequency converter according to claim 5, characterized in that, in, Determining the zero-crossing point of the inverter based on its output voltage includes: The maximum and minimum values ​​of the inverter's output voltage obtained after a set number of consecutive iterations are determined and denoted as the inverter's maximum output voltage and minimum output voltage. If it is determined that the product of the inverter's maximum output voltage and the inverter's minimum output voltage is greater than 0, then the time period during which the inverter's output voltage is obtained for a set number of consecutive times is determined as the inverter's zero-crossing point. Wherein, if the maximum output voltage of the inverter is obtained before the minimum output voltage of the inverter, then the zero-crossing point of the inverter is determined to be the zero-crossing point of the transition from the positive half-cycle to the negative half-cycle; if the minimum output voltage of the inverter is obtained before the maximum output voltage of the inverter, then the zero-crossing point of the inverter is determined to be the zero-crossing point of the transition from the negative half-cycle to the positive half-cycle. And / or, Determining the dead-zone compensation voltage of the inverter at its zero-crossing point includes: The difference between the ideal output voltage of the inverter and the output voltage of the inverter obtained at the zero-crossing point of the inverter is recorded as the output voltage difference of the inverter. The dead-zone compensation voltage of the inverter is determined by multiplying the ratio of the output voltage difference of the inverter to the ideal output voltage of the inverter with the amplitude of the triangular carrier wave of the inverter. The dead-zone compensation voltage of the inverter is then superimposed on the waveform of the SVPWM modulation output of the inverter to perform dead-zone compensation on the inverter, so as to realize dynamic dead-zone compensation control of the inverter in the energy feedback stage.

7. A control device for a frequency converter, characterized in that, include: The acquisition unit is configured to acquire the bus voltage of the inverter, the output current of the inverter, and the output voltage of the inverter when the inverter enters the energy feedback stage. The control unit is configured to determine the zero-crossing point and the dead-zone compensation voltage of the inverter based on the bus voltage of the inverter, the output current of the inverter, and the output voltage of the inverter. The control unit is also configured to perform dead-zone compensation on the inverter at the zero-crossing point of the inverter using the dead-zone compensation voltage of the inverter, so as to realize dynamic dead-zone compensation control of the inverter during the energy feedback stage.

8. A magnetic levitation system, characterized in that, include: The control device for the frequency converter as described in claim 7.

9. A storage medium, characterized in that, The storage medium includes a stored program, wherein, when the program is executed, the device containing the storage medium is controlled to perform the control method of the frequency converter as described in any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the control method for the frequency converter as described in any one of claims 1 to 6.

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