Permanent magnet synchronous motor frequency conversion soft start and grid connection device and control method

Abstract

The invention provides a permanent magnet synchronous motor frequency conversion soft start and grid connection device and a control method. The device comprises a power supply grid (1), a permanent magnet synchronous motor (2), three-phase contactors (3), (4) and (5), a variable frequency controller composed of a rectifier (6), an inverter (7) and a control panel (8), a voltage sampling module (9), a current sampling module (10) and a filter inductor (11) at the output end of the inverter. One end of the three-phase contactor (3) is connected with a three-phase inlet wire of the power supply grid (1), and the other end of the three-phase contactor (3) is connected with the input end of the rectifier (6); one end of the three-phase contactor (4) is connected with the output end of the inverter (7), and the other end of the three-phase contactor (4) is connected with the input end of the motor (2); and one end of the three-phase contactor (5) is connected with a three-phase inlet wire of the power supply grid (1). VF open-loop pre-synchronization control is introduced in advance in vector control, power grid synchronization conditions are simulated, a motor is enabled to actively match power grid magnetic field parameters before grid connection, smooth transition of a control mode is realized, and large impact current and electromechanical oscillation are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet synchronous motors, and in particular to a variable frequency soft starting and grid-connected device and a control method for a permanent magnet synchronous motor. Background Art

[0002] A permanent magnet synchronous motor is a synchronous motor that uses permanent magnets (rather than electromagnetic coils) to generate its rotor magnetic field. A variable frequency soft start is a control method that uses a frequency converter to gradually adjust the frequency and voltage of the motor's input power supply, allowing the motor to smoothly accelerate from a stationary state to the rated speed. A grid-connected device is a hardware system that enables the motor to switch from frequency converter power supply (variable frequency mode) to industrial frequency grid power supply (grid-connected mode).

[0003] Permanent magnet synchronous motors (PMSMs) are widely used in new energy, industrial drives, transportation, and other fields due to their outstanding advantages, including high efficiency, energy saving, high power density, excellent speed regulation, and high reliability. Starting control technology for PMSMs plays a key role in their widespread application.

[0004] The traditional direct starting method of permanent magnet synchronous motors generates large inrush currents, which not only damage the motor's lifespan and performance but also seriously threaten the stability of the power grid. Especially in high-power applications, excessive inrush currents can even damage the motor. For applications requiring on-load starting, a variable frequency soft starting solution is generally used. This involves using a variable frequency controller to start the motor before connecting it to the grid. This variable frequency soft starting method effectively controls the motor's starting current and protects the motor.

[0005] A permanent magnet synchronous motor variable frequency soft start and grid connection control method in the prior art includes: using a synchronous rotating coordinate system phase-locked loop (SRF-PLL) to obtain the modulus and angle of the grid voltage, and monitoring the modulus and angle of the motor voltage through coordinate transformation and voltage amplitude-angle transformation. The DSP is used to determine in real time whether the difference in amplitude, phase, and frequency between the variable frequency controller and the three-phase voltage of the grid meets the grid connection conditions for grid connection switching.

[0006] Another medium- and high-voltage synchronous motor automatic variable-frequency soft-start method in the prior art includes: performing amplitude modulation and phase locking after the medium- and high-voltage synchronous motor is variable-frequency started: obtaining the grid voltage amplitude through the grid line voltage amplitude and the zero-crossing detection circuit, controlling the excitation full-controlled rectifier circuit through a second controller to adjust the current of the excitation winding so that the grid voltage amplitude is the same as the motor back electromotive force amplitude; adjusting the control angle of the three-phase full-controlled rectifier circuit and the inversion angle of the three-phase full-controlled inverter circuit so that the phase of the motor is the same as the phase of the grid; and switching to the grid after the conditional grid connection conditions are met.

[0007] Another method for suppressing the inrush current during the switching process of an asynchronous motor variable frequency soft starter in the prior art includes: after the variable frequency soft starter drags the asynchronous motor to the rated speed, a phase-locked loop is used to phase-lock the AC grid voltage U1 to obtain its phase and amplitude, and the AC grid sampled voltage is filtered to compensate for the phase and amplitude, and then amplitude modulation and phase locking are performed.

[0008] The voltage phase difference between the motor back electromotive force U2 and the AC grid voltage U1 is used as an additional control quantity for the speed set value of the speed control loop, and the voltage amplitude difference between the motor back electromotive force U2 and the AC grid voltage U1 is used as an additional control quantity for the flux set value of the flux control loop, so as to adjust the output voltage phase and amplitude so that the phase difference and amplitude difference are reduced to an acceptable dynamic range.

[0009] Drawbacks of the aforementioned conventional permanent magnet synchronous motor control methods include: The traditional phase-locked loop (PLL) lacks harmonic interference immunity and cannot effectively suppress harmonic components in the grid voltage, leading to phase tracking errors. This phase error directly affects the accuracy of the motor's vector control and causes distortion in the grid-connected current waveform.

[0010] Traditional grid-connected switching adopts a hard switching strategy of "closed-loop vector control → open-loop operation", which leads to amplitude / phase mismatch between the stator magnetic field and the grid magnetic field, causing impact current and electromechanical oscillation, threatening equipment safety.

[0011] When a frequency converter is connected in parallel with the industrial frequency grid, the PWM (Pulse Width Modulation) pulse wave and the fundamental wave are superimposed to generate medium and high frequency harmonic currents, which increases the losses of the frequency converter and deteriorates the power quality of the grid. Summary of the Invention

[0012] The embodiments of the present invention provide a variable frequency soft starting and grid-connected device and control method for a permanent magnet synchronous motor, thereby effectively improving the control accuracy and grid-connected current quality of the permanent magnet synchronous motor.

[0013] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions.

[0014] According to one aspect of the present invention, a permanent magnet synchronous motor variable frequency soft start and grid connection device is provided, comprising: a power supply grid (1), a permanent magnet synchronous motor (2), a three-phase contactor (3) (4) (5), a variable frequency controller composed of a rectifier (6), an inverter (7) and a control board (8), a voltage sampling module (9), a current sampling module (10) and a filter inductor (11) at the output end of the inverter;

[0015] One end of the three-phase contactor (3) is connected to the three-phase incoming line of the power supply network (1), and the other end of the three-phase contactor (3) is connected to the input end of the rectifier (6); one end of the three-phase contactor (4) is connected to the output end of the inverter (7), and the other end of the three-phase contactor (4) is connected to the input end of the motor (2); one end of the three-phase contactor (5) is connected to the three-phase incoming line of the power supply network (1), and the other end of the three-phase contactor (5) is connected to the motor input end (2).

[0016] Preferably, the rectifier (6) of the frequency conversion controller is a three-phase uncontrolled rectifier, the inverter (7) is a three-phase two-level insulated gate bipolar transistor (IGBT) inverter, and the control board (8) includes a power supply module, a human-machine interaction module, an analog / digital conversion module, a contactor drive module, and a control switch module; the control chip of the control board (8) uses a digital signal processing technology DSP chip to realize the control function.

[0017] Preferably, the voltage sampling module (9) collects the line voltage of the power supply grid (1) and the DC bus voltage provided by the rectifier (6), and inputs the collected voltage into the control board (8) through the analog / digital conversion module;

[0018] The current sampling module (10) collects the three-phase current at the output end of the inverter (7), and inputs the collected three-phase current into the control board (8) through the analog / digital conversion module;

[0019] The filter inductor (11) is connected between the contactor (4) and the output end of the inverter (7) and is used for current suppression when the industrial frequency and variable frequency power supplies are operated in parallel.

[0020] According to another aspect of the present invention, a method for variable frequency soft starting and grid-connected control of a permanent magnet synchronous motor is provided, comprising:

[0021] Step S1: Close contactor (3) and contactor (4), and the power grid supplies power to the frequency conversion controller;

[0022] Step S2: Obtain the actual three-phase current i of the motor through the Hall current sensor a 、i b and i c , calculate the motor phase θ through the position-free algorithm e and speed ω e , after coordinate transformation, we can get the actual i d and i q ;

[0023] Step S3: Given the permanent magnet synchronous motor speed command value ω*, use the vector control method to obtain the torque current command value through the speed outer loop Given excitation current command Obtained through the current inner loop and After the coordinate transformation, pulse width modulation is performed to generate a pulse width signal, which is input into the inverter to realize variable frequency starting of the permanent magnet synchronous motor;

[0024] Step S4: Obtain the instantaneous value of the grid voltage through the voltage sampling module, use the SOGI-PLL phase-locked loop technology to phase-lock the grid voltage, and obtain the real-time amplitude of the grid voltage u g and phase θ g ;

[0025] Step S5: After the motor starts to the rated speed, the motor is phase-locked and controlled according to the grid voltage phase θ g , calculate the variable u related to the angle error through synchronous coordinate transformation q_est , calculate the compensation amount ω of the motor speed cmp ;

[0026] Step S6: Determine whether the current phase difference between the motor and the grid and the motor operating frequency meet the conditions for switching to an open loop. If so, proceed to step S7. If not, return to step S5.

[0027] Step S7: Calculate the motor terminal voltage vector amplitude u under vector control si , according to the real-time amplitude u of the grid voltage obtained from step S4 g and phase θ g , switch the motor control mode to open-loop VF control, the amplitude and phase of the open-loop VF control are directly given;

[0028] Step S8: Determine whether the current amplitude difference between the motor and the grid meets the grid connection conditions. If yes, proceed to step 9; otherwise, return to step 7.

[0029] Step S9: closing the contactor (5), at which point the variable frequency power supply and the industrial frequency power supply are operated in parallel, and a three-phase inductor (11) is connected in series to the inverter end of the device to suppress the harmonic current between the two voltage sources;

[0030] Step S10: Add a current loop to control the harmonic current between the two voltage sources, and set the current loop command value to The actual current obtained in step S2 is used for current closed-loop control to further suppress the harmonic current between the two voltage sources and transfer the motor supply current to the power grid;

[0031] Step S11: disconnect contactor (3) and contactor (4), and the permanent magnet synchronous motor is connected to the grid for operation, and the motor is independently powered by the grid.

[0032] Preferably, in step S2, the phase θ of the motor is obtained by a position-free algorithm. e and speed ω e The calculation formula is:

[0033]

[0034] ω e =k pL θ err +k iL ∫θ err dt

[0035] θ e =∫ω e dt+θ0

[0036] Where θ err is the rotor position error, and is the back EMF in the dq axis coordinate system estimated by the back EMF observer, k pL k is the proportional coefficient of the position phase-locked loop, iL is the integral coefficient of the position phase-locked loop, θ0 is the initial phase of the motor;

[0037] Coordinate transformation to obtain actual i d and i q The calculation formula is:

[0038]

[0039] Preferably, in step S5, the variable u related to the angle error is q_est and the speed compensation ω cmp The calculation formula is as follows:

[0040]

[0041] ω cmp =-K ω u q_est (2)

[0042] In formula (1), u q_est is the estimated value of the q-axis voltage in the rotating coordinate system of the grid phase, and To modulate the three-phase reference voltage, θ g is the grid phase, K in formula (2) ω is the proportional coefficient of the motor phase-locked loop.

[0043] Preferably, in step S6, the switching conditions for switching the motor from vector control to open-loop VF control are: the phase difference between the motor and the grid is within 0.5°, and the actual operating frequency of the motor is within 49.95Hz-50.05Hz.

[0044] Preferably, in step S7, u si is the voltage vector amplitude of the motor at the moment of switching from closed loop to open loop, which is calculated by the following formula:

[0045]

[0046] In formula (3), and It is the reference value of the dq axis voltage of closed-loop control.

[0047] Preferably, in step S7, the amplitude and phase of the three-phase voltage modulated by the motor open-loop control are given by the following formula:

[0048]

[0049] u t =u t +K v e v (5)

[0050] e v =u g -u si (6)

[0051] In formula (4) and To modulate the three-phase reference voltage, u t The open-loop control voltage amplitude is obtained from formula (5), θ g is the grid phase, K in formula (4) v is the voltage transition coefficient, e v is the voltage error when switching open loop, that is, the grid voltage u g The voltage vector amplitude u of the motor when switching open loop si The difference is obtained by formula (6).

[0052] Preferably, in step S8, the switching condition for the motor to be connected to the grid is that the amplitude difference between the motor and the grid is within 1V.

[0053] As can be seen from the technical solutions provided by the aforementioned embodiments of the present invention, the present invention eliminates grid-connection transient shocks and electromechanical oscillations. By pre-introducing VF open-loop presynchronization control into vector control, grid synchronization conditions are simulated, enabling the motor to actively match the grid magnetic field parameters (amplitude deviation <2%, phase difference <5) before grid connection. This enables a smooth control mode transition and avoids large inrush currents (peak value <120% of rated current) and electromechanical oscillations (speed fluctuation <5%).

[0054] Additional aspects and advantages of the present invention will be set forth in part in the following description, will be obvious from the following description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0056] Figure 1 A structural diagram of a variable frequency soft starting and grid-connected device for a permanent magnet synchronous motor provided by an embodiment of the present invention;

[0057] Figure 2 A schematic diagram illustrating a method for variable frequency soft starting and grid-connected control of a permanent magnet synchronous motor provided by an embodiment of the present invention;

[0058] Figure 3 A specific processing flow chart of a variable frequency soft starting and grid-connected control method for a permanent magnet synchronous motor provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0060] It will be understood by those skilled in the art that, unless expressly stated otherwise, the singular forms "a", "an", "said" and "the" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the description of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, "connected" or "coupled" as used herein may include wireless connections or couplings. The term "and / or" used herein includes any unit and all combinations of one or more associated listed items.

[0061] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention pertains. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such herein, will not be interpreted in an idealized or overly formal sense.

[0062] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings, and each embodiment does not constitute a limitation on the embodiments of the present invention.

[0063] The structure diagram of a permanent magnet synchronous motor variable frequency soft start and grid connection device provided by the embodiment of the present invention is as follows Figure 1 As shown, it includes a power supply grid (1), a permanent magnet synchronous motor (2), a three-phase contactor (3) (4) (5), a frequency conversion controller composed of a rectifier (6), an inverter (7) and a control board (8), a voltage sampling module (9), a current sampling module (10) and a filter inductor (11) at the output end of the inverter.

[0064] One end of the three-phase contactor (3) is connected to the three-phase incoming line of the power grid (1), and the other end of the three-phase contactor (3) is connected to the input end of the rectifier (6); one end of the three-phase contactor (4) is connected to the output end of the inverter (7), and the other end of the three-phase contactor (4) is connected to the input end of the motor (2); one end of the three-phase contactor (5) is connected to the three-phase incoming line of the power grid (1), and the other end of the three-phase contactor (5) is connected to the motor input end (2).

[0065] The rectifier (6) of the frequency conversion controller is a three-phase uncontrolled rectifier, the inverter (7) is a three-phase two-level IGBT (Insulated Gate Bipolar Transistor) inverter, and the control board (8) includes a power supply module, a human-machine interaction module, an analog / digital conversion module, a contactor drive module and a control switch module; the control chip of the control board (8) uses a DSP (Digital Signal Processing) chip to realize the control function.

[0066] The voltage sampling module (9) collects the line voltage of the power supply grid (1) and the DC bus voltage provided by the rectifier (6), and inputs the collected voltage into the control board (8) through the analog / digital conversion module.

[0067] The current sampling module (10) collects the three-phase current at the output end of the inverter (7), and inputs the collected three-phase current into the control board (8) through the analog / digital conversion module.

[0068] The filter inductor (11) is connected between the contactor (4) and the output end of the inverter (7) and is used for current suppression when the industrial frequency and variable frequency power supplies are operated in parallel.

[0069] The power supply module in the control board (8) provides energy support for the chip. The human-computer interaction module is used to realize two-way information interaction between the user and the DSP system, including data uploading and command issuance. The analog / digital conversion module is used to convert analog sensor signals into digital signals that can be processed by the DSP. The contactor drive module is used to control the opening and closing of the contactor in the device. The control switch module is used to control the output of the main circuit and play a protective role.

[0070] The implementation principle of a variable frequency soft start and grid-connected control method for a permanent magnet synchronous motor provided by the embodiment of the present invention is as follows: Figure 2 As shown, the control method includes the following parts: motor variable frequency soft start control, grid phase-locked control, motor phase-locked control, closed-loop open-loop condition judgment, motor VF (voltage and frequency) open-loop control, grid connection condition judgment, inverter and grid parallel operation control and motor grid connection operation.

[0071] The specific processing flow of a permanent magnet synchronous motor variable frequency soft start and grid connection control method provided by the embodiment of the present invention is as follows: Figure 3 As shown, the processing steps include the following:

[0072] Step S1: Close contactor KM1, and the three-phase voltage of the grid is supplied to the DC bus voltage u through the uncontrolled rectifier. dc , obtain the voltage value u through the voltage sampling module dc , and input into the control chip in the control board through the analog / digital conversion module; close the contactor KM2, the inverter output is connected to the motor end, and the motor is powered by the inverter.

[0073] Step S2: Obtain the actual three-phase current i of the motor through the Hall current sensor a 、i b and i c , input into the control chip through the analog / digital conversion module, and the motor phase θ is calculated by the position-free algorithm e and speed ω e , with the motor phase θ e For synchronous rotation coordinate system, the actual i is obtained after coordinate transformation d and i q ;

[0074] Obtain the motor phase θ through the position-free algorithm e and speed ω e The calculation formula is:

[0075]

[0076] ω e =k pL θ err +k iL ∫θ err dt

[0077] θ e =∫ω e dt+θ0

[0078] Where θ err is the rotor position error, and is the back EMF in the dq axis coordinate system estimated by the back EMF observer, k pL k is the proportional coefficient of the position phase-locked loop, iL is the integral coefficient of the position phase-locked loop, and θ0 is the initial phase of the motor.

[0079] Coordinate transformation to obtain actual i d and i q The calculation formula is:

[0080]

[0081] Step S3: Give the permanent magnet synchronous motor speed command value ω * , using the vector control method, the torque current command value i is obtained through the speed outer loop q * , given the excitation current instruction i d * =0, the direct axis command voltage is obtained through the current inner loop and quadrature axis command voltage After the coordinate transformation, pulse width modulation is performed to generate a pulse width signal, which is input into the inverter to realize variable frequency starting of the permanent magnet synchronous motor.

[0082] Torque current command value i q * The calculation formula is

[0083]

[0084] Where k pS is the proportional coefficient of the speed loop, k iS is the integral coefficient of the speed loop, N p is the number of motor pole pairs, ψ f is the motor flux.

[0085] and The specific calculation formula is:

[0086]

[0087] Where k pI is the proportional coefficient of the current loop, k iI is the integral coefficient of the current loop.

[0088] Step S4: Power grid phase-locked control:

[0089] Obtain the instantaneous value of the grid line voltage u through the voltage sampling module ab 、u bc and u ca , the instantaneous voltage value u ab 、u bc and u ca After the conversion by the analog / digital conversion module, the voltage is input to the control chip in the control board. The control chip generates the voltage according to the instantaneous value u ab 、u bc and u ca The high-performance second-order generalized integrator-phase lock loop (SOGI-PLL) technology is used to phase-lock the grid voltage and obtain the real-time amplitude of the grid voltage u. g and phase θ g ;

[0090] Step S5: Motor phase-locked control:

[0091] After the motor starts to the rated speed, the motor phase lock control is performed, and the grid voltage phase θ is obtained. g , calculate the variable u related to the angle error q_est That is, the estimated value of the q-axis voltage in the grid phase synchronization coordinate system is shown in the following formula:

[0092]

[0093] Where, and To modulate the three-phase reference voltage, θ g is the grid phase.

[0094] According to the estimated value u of the q-axis voltage in the grid phase synchronization coordinate system q_est , the required motor speed compensation can be calculated as shown below:

[0095] ω cmp =-K ω v q_est (2)

[0096] Where K ω is the proportional coefficient of the motor phase-locked loop.

[0097] Step S6: Determine whether the current phase difference between the motor and the grid and the motor operating frequency meet the conditions for switching to open loop. The switching conditions are that the phase difference between the motor and the grid is within 0.5° and the actual motor operating frequency is within 49.95Hz-50.05Hz. If these conditions are met, proceed to step 7; if not, return to step 5.

[0098] 4. Motor VF open loop control:

[0099] Step S7: Calculate the motor terminal voltage vector amplitude u under vector control si , as shown below:

[0100]

[0101] Where, and is the reference value of the dq axis voltage of the closed loop control. After switching to open loop, u si Fixed to the voltage vector amplitude of the motor at the moment of switching from closed loop to open loop.

[0102] According to the real-time amplitude u of the grid voltage obtained from step S4 g and phase θ g , switch the motor control mode to open-loop VF control, and the amplitude and phase of the open-loop control are directly given as shown in the following formula:

[0103]

[0104] u t =u t +K v e v (5)

[0105] e v =u g -u si (6)

[0106] In formula (4) and To modulate the three-phase reference voltage, u t The open-loop control voltage amplitude is obtained from formula (5), θ g is the grid phase, K in formula (4) v is the voltage transition coefficient, e v is the voltage error when switching open loop, that is, the grid voltage u g The voltage vector amplitude u of the motor when switching open loop si The difference is obtained by formula (6).

[0107] Step S8: Determine whether the current amplitude difference between the motor and the grid meets the grid connection condition. The switching condition is that the amplitude difference between the motor and the grid is within 1V. If this condition is met, go to step 9. If not, return to step 7.

[0108] Step S9: Control of the parallel operation of the inverter and the power grid: Close the contactor KM3. At this time, the variable frequency power supply and the industrial frequency power supply operate in parallel. The three-phase inductor connected in series at the inverter end of the device can effectively suppress the harmonic current between the two voltage sources.

[0109] Step S10: Add a current loop to further control the harmonic current between the two voltage sources, and set the current loop command value to i d * =0, i q * =0, the actual current i obtained in step 2 d and i q Perform current closed-loop control to further suppress harmonic currents between the two voltage sources and quickly transfer the motor supply current to the grid;

[0110] 6. Motor grid-connected operation

[0111] Step S11: disconnect contactor KM1 and contactor KM2, and the permanent magnet synchronous motor is connected to the grid for operation, and the motor is independently powered by the grid.

[0112] In summary, the present invention achieves precise synchronous control through high-precision grid phase locking, impact-free grid-connected switching, avoidance of electromechanical transient effects, low-cost and high-efficiency harmonic suppression, compatibility with high-power scenarios, and system compatibility and scalability through high-precision grid phase locking.

[0113] This invention improves phase-locking accuracy and harmonic interference immunity. By using a second-order generalized integrator-phase lock loop (SOGI-PLL) to directly generate a positive-sequence signal and filter out harmonics during the phase-locking process, eliminating the need for additional harmonic separation algorithms, it ensures accurate, real-time extraction of the grid voltage phase and amplitude, thereby improving motor control accuracy and grid-connected current quality.

[0114] Those skilled in the art will appreciate that the accompanying drawings are merely schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required to implement the present invention.

[0115] Each embodiment in this specification is described in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the device or system embodiments, since they are basically similar to the method embodiments, the description is relatively simple. For the relevant parts, refer to the partial description of the method embodiments. The device and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. A person of ordinary skill in the art can understand and implement it without making any creative efforts.

[0116] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A permanent magnet synchronous motor variable frequency soft starting and grid-connected device, characterized in that: include: A power supply grid (1), a permanent magnet synchronous motor (2), a three-phase contactor (3) (4) (5), a frequency conversion controller composed of a rectifier (6), an inverter (7) and a control board (8), a voltage sampling module (9), a current sampling module (10) and a filter inductor (11) at the output end of the inverter; One end of the three-phase contactor (3) is connected to the three-phase incoming line of the power supply network (1), and the other end of the three-phase contactor (3) is connected to the input end of the rectifier (6); one end of the three-phase contactor (4) is connected to the output end of the inverter (7), and the other end of the three-phase contactor (4) is connected to the input end of the motor (2); one end of the three-phase contactor (5) is connected to the three-phase incoming line of the power supply network (1), and the other end of the three-phase contactor (5) is connected to the motor input end (2).

2. The device according to claim 1, characterized in that The rectifier (6) of the frequency conversion controller is a three-phase uncontrolled rectifier, the inverter (7) is a three-phase two-level insulated gate bipolar transistor (IGBT) inverter, and the control board (8) includes a power supply module, a human-machine interaction module, an analog / digital conversion module, a contactor drive module, and a control switch module; the control chip of the control board (8) uses a digital signal processing technology DSP chip to realize the control function.

3. The device according to claim 1, characterized in that The voltage sampling module (9) collects the line voltage of the power supply grid (1) and the DC bus voltage provided by the rectifier (6), and inputs the collected voltage into the control board (8) through the analog / digital conversion module; The current sampling module (10) collects the three-phase current at the output end of the inverter (7), and inputs the collected three-phase current into the control board (8) through the analog / digital conversion module; The filter inductor (11) is connected between the contactor (4) and the output end of the inverter (7) and is used for current suppression when the industrial frequency and variable frequency power supplies are operated in parallel.

4. A method for variable frequency soft starting and grid-connected control of a permanent magnet synchronous motor, characterized in that: include: Step S1: Close contactor (3) and contactor (4), and the power grid supplies power to the frequency conversion controller; Step S2: Obtain the actual three-phase current i of the motor through the Hall current sensor a 、i b and i c , calculate the motor phase θ through the position-free algorithm e and speed ω e , after coordinate transformation, we can get the actual i d and i q ; Step S3: Given the permanent magnet synchronous motor speed command value ω*, use the vector control method to obtain the torque current command value through the speed outer loop Given excitation current command Obtained through the current inner loop and After the coordinate transformation, pulse width modulation is performed to generate a pulse width signal, which is input into the inverter to realize variable frequency starting of the permanent magnet synchronous motor; Step S4: Obtain the instantaneous value of the grid voltage through the voltage sampling module, use the SOGI-PLL phase-locked loop technology to phase-lock the grid voltage, and obtain the real-time amplitude of the grid voltage u g and phase θ g ; Step S5: After the motor starts to the rated speed, the motor is phase-locked and controlled according to the grid voltage phase θ g , calculate the variable u related to the angle error through synchronous coordinate transformation q_est , calculate the compensation amount ω of the motor speed cmp ; Step S6: Determine whether the current phase difference between the motor and the grid and the motor operating frequency meet the conditions for switching to an open loop. If so, proceed to step S7. If not, return to step S5. Step S7: Calculate the motor terminal voltage vector amplitude u under vector control si , according to the real-time amplitude u of the grid voltage obtained from step S4 g and phase θ g , switch the motor control mode to open-loop VF control, the amplitude and phase of the open-loop VF control are directly given; Step S8: Determine whether the current amplitude difference between the motor and the grid meets the grid connection conditions. If yes, proceed to step 9; otherwise, return to step 7. Step S9: closing the contactor (5), at which point the variable frequency power supply and the industrial frequency power supply are operated in parallel, and a three-phase inductor (11) is connected in series to the inverter end of the device to suppress the harmonic current between the two voltage sources; Step S10: Add a current loop to control the harmonic current between the two voltage sources, and set the current loop command value to The actual current obtained in step S2 is used for current closed-loop control to further suppress the harmonic current between the two voltage sources and transfer the motor supply current to the power grid; Step S11: disconnect contactor (3) and contactor (4), and the permanent magnet synchronous motor is connected to the grid for operation, and the motor is independently powered by the grid.

5. The method according to claim 4, characterized in that: In step S2, the phase θ of the motor is obtained by the position-free algorithm. e and speed ω e The calculation formula is: ω e =k pL θ err +k iL ∫θ err dt i e =∫ω e dt+θ0 Where θ err is the rotor position error, and is the back EMF in the dq axis coordinate system estimated by the back EMF observer, k pL k is the proportional coefficient of the position phase-locked loop, iL is the integral coefficient of the position phase-locked loop, θ0 is the initial phase of the motor; Coordinate transformation to obtain actual i d and i q The calculation formula is:

6. The method according to claim 4, characterized in that: In step S5, the variable u related to the angle error q_est and the speed compensation ω cmp The calculation formula is as follows: ω cmp =-K ω u q_est (2) In formula (1), u q_est is the estimated value of the q-axis voltage in the rotating coordinate system of the grid phase, and To modulate the three-phase reference voltage, θ g is the grid phase, K in formula (2) ω is the proportional coefficient of the motor phase-locked loop.

7. The method according to claim 4, characterized in that: In step S6, the switching conditions for the motor to switch from vector control to open-loop VF control are: the phase difference between the motor and the grid is within 0.5°, and the actual operating frequency of the motor is within 49.95Hz-50.05Hz.

8. The method according to claim 4, wherein: In step S7, u si is the voltage vector amplitude of the motor at the moment of switching from closed loop to open loop, which is calculated by the following formula: In formula (3), and It is the reference value of the dq axis voltage of closed-loop control.

9. The method according to claim 4, wherein: In step S7, the amplitude and phase of the three-phase voltage modulated by the motor open-loop control are given by the following formula: in t =in t +K v yes v (5) yes v =in g -in si (6) In formula (4) and To modulate the three-phase reference voltage, u t The open-loop control voltage amplitude is obtained from formula (5), θ g is the grid phase, K in formula (4) v is the voltage transition coefficient, e v is the voltage error when switching open loop, that is, the grid voltage u g The voltage vector amplitude u of the motor when switching open loop si The difference is obtained by formula (6).

10. The method according to claim 4, characterized in that: In step S8, the switching condition for the motor to be connected to the grid is that the amplitude difference between the motor and the grid is within 1V.

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