Power-on surge suppression control circuit and control method of variable frequency driver

Abstract

The invention provides a power-on surge suppression control circuit and control method for a variable frequency driver, and the control circuit comprises a rectification module which provides a DC power supply; the bus voltage sampling module is connected with the rectification module and is used for sampling bus voltage so as to obtain two paths of DC bus voltage sampling values; the hardware hysteresis control module is connected with the bus voltage sampling unit and used for receiving the two paths of DC bus voltage sampling values and outputting PTC control signals based on the two paths of bus voltage values; and the power-on surge control module is respectively connected with the rectifier module and the hardware hysteresis control module, and is used for receiving the hysteresis control signal and controlling a PTC resistor to be connected into or connected out of the rectifier module based on the PTC control signal. The reliable self-adaptive variable frequency driver PTC power-on surge suppression control circuit is realized, hardware automatic control is realized in the power-on and power-off processes of the power supply, and DSP port resources are saved.

Description

Technical Field

[0001] The present application belongs to the technical field of switching power supplies and relates to a power-on surge suppression control circuit and a control method for a variable frequency drive. Background Art

[0002] With the continuous development and maturity of power electronics technology and the continuous expansion of the HVAC (Heating Ventilation and Air Conditioning) market, the application of variable frequency drives has become more and more extensive, expanding from traditional household fields to commercial fields. The product application fields are also increasing, including air conditioners, elevators, automobiles, heat pumps, photovoltaics, wind power generation, etc. Inverters are almost used in all areas of power and electricity, with power ranges from tens of watts to hundreds of kilowatts or even higher. The energy storage capacitors required for drives of different powers are different in size. Due to the characteristics of capacitors, the larger the capacitance, the smaller the capacitive reactance. When powered on, due to the volt-ampere characteristics, the instantaneous current is very large, almost equivalent to a short circuit, which will cause damage to the power devices on the rectifier side of the drive and the protective air switch on the user side. Therefore, the current mainstream practice is to insert a current-limiting PTC resistor in the front-end rectifier circuit to slowly pre-charge the electrolytic capacitor, and then bypass the current-limiting resistor through the software-controlled relay to start the normal operation of the inverter.

[0003] However, this control method requires the cooperation of software and hardware to be realized. The entire function needs to occupy multiple ports of DSP, which occupies a certain degree of PCB layout and DSP resources. In some projects with limited DSP port resources, it may face the problem of replacing more DSP pins. At the same time, the long-distance transmission of sampling signals and control signals also has potential anti-interference risks. Summary of the invention

[0004] The present application provides a power-on surge suppression control circuit and a control method for a variable frequency drive, which are used to solve the problem of DSP port resource shortage caused by the need to suppress the power-on surge through multiple DSP ports during the startup process of the inverter drive circuit.

[0005] In the first aspect, the present application provides a power-on surge suppression control circuit for a variable frequency drive. The control circuit includes: a rectifier module, a bus voltage sampling module, a hardware hysteresis control module and a power-on surge control module; wherein the rectifier module provides a DC power supply; the bus voltage sampling module is connected to the rectifier module, and is used to sample the bus voltage to obtain two DC bus voltage sampling values; the hardware hysteresis control module is connected to the bus voltage sampling unit, and is used to receive the two DC bus voltage sampling values, and output a PTC control signal based on the two bus voltage values; the power-on surge control module is respectively connected to the rectifier module and the hardware hysteresis control module, and is used to receive the hysteresis control signal, and control the PTC resistor to be connected to or connected out of the rectifier module based on the PTC control signal.

[0006] In an implementation of the first aspect, the bus voltage sampling module includes: a first sampling unit and a second sampling unit; wherein the first sampling unit and the second sampling unit are commonly connected to the output end of the rectifier module; the first sampling unit outputs the first DC bus voltage sampling value, and the second sampling unit outputs the second bus voltage value.

[0007] In an implementation of the first aspect, the first sampling unit includes: a first voltage-dividing resistor group, a first operational amplifier, and a first capacitor; one end of the first voltage-dividing resistor group is connected to the positive output of the rectifier module, and the other end is connected to the negative output of the rectifier module; the positive input end of the first operational amplifier is connected to the first voltage-dividing resistor group, the negative input end of the first operational amplifier is connected between one end of the first capacitor and a switching power supply, the negative input end of the first operational amplifier is also connected to the output end of the first operational amplifier, and the input end of the first operational amplifier and the other end of the first capacitor are grounded.

[0008] In an implementation of the first aspect, the second sampling unit includes: a second voltage-dividing resistor group; one end of the second voltage-dividing resistor group is connected to the positive output of the rectifier module, and the other end is connected to the negative output of the rectifier module.

[0009] In an implementation of the first aspect, the hardware hysteresis control module includes: a hysteresis comparison unit and a comparator unit; wherein the hysteresis comparison unit is connected to the bus voltage sampling module, and is used to receive the two bus voltage values, and output a hysteresis control signal based on the two bus voltage values; the comparator unit is connected to the hysteresis comparison unit, and is used to receive the hysteresis control signal, and output a PTC control signal based on the hysteresis control signal.

[0010] In an implementation of the first aspect, the hysteresis comparison unit includes: a second operational amplifier, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor and a second capacitor; one end of the third resistor is connected to the first DC bus voltage output by the bus voltage sampling module, and the other end is connected to the positive input terminal of the second operational amplifier; one end of the fourth resistor is connected to the second DC bus voltage output by the bus voltage sampling module, and the other end is connected to the negative input terminal of the second operational amplifier; one end of the fifth resistor is connected to one end of the sixth resistor, the other end of the fifth resistor is connected to the switching power supply, and the other end of the sixth resistor is connected to the output terminal of the second operational amplifier; the positive input terminal of the second operational amplifier is also connected to the connecting line between one end of the fifth resistor and the other end of the sixth resistor, the negative input terminal of the second operational amplifier is also connected to one end of the second capacitor, and the other end of the second capacitor is grounded.

[0011] In an implementation of the first aspect, the comparator unit includes: a third operational amplifier, a seventh resistor, an eighth resistor, a ninth resistor and a third capacitor; one end of the seventh resistor is connected to the output end of the hysteresis comparison unit, and the other end is connected to the negative input end of the third operational amplifier, one end of the eighth resistor is connected to the switching power supply, and the other end is connected to one end of the ninth resistor, and the other end of the ninth resistor is grounded; the positive input end of the third operational amplifier is connected to the connecting line between the other end of the eighth resistor and one end of the ninth resistor, the negative input end of the third operational amplifier and one end of the third capacitor are commonly connected to the switching power supply, the other end of the third capacitor is grounded, and the output end of the third operational amplifier is connected to the power-on surge control module.

[0012] In an implementation of the first aspect, the power-on surge control module includes a relay, and the rectifier module includes a PTC resistor; the two ends of the switch of the relay are respectively connected to the two ends of the PTC resistor, and the input end of the relay receives the PTC control signal output by the hardware hysteresis control module to control the closing or opening of the switch of the relay.

[0013] In an implementation of the first aspect, the PTC control signal includes: a PTC high-level control signal and a PTC low-level control signal; the power-on surge control module controls the relay to be energized based on the PTC high-level control signal so that the PTC resistor is connected out of the rectifier module; the power-on surge control module controls the relay to be disconnected based on the PTC low-level control signal so that the PTC resistor is connected to the rectifier module.

[0014] In a second aspect, the present application provides a power-on surge suppression control method for a variable frequency drive. The control method includes: sampling the bus voltage and obtaining a first DC bus voltage sampling value and a second DC bus voltage sampling value; outputting a PTC control signal based on the first DC bus voltage sampling value and the second DC bus voltage sampling value; and controlling the PTC resistor to be connected to or connected out of the control circuit according to the PTC control signal.

[0015] As described above, the power-on surge suppression control circuit and control method of the variable frequency drive described in the present application have the following beneficial effects:

[0016] The present application realizes a reliable and adaptive hardware implementation method of PTC power-on surge suppression control for variable frequency drive by setting two voltage sampling units with inconsistent sampling coefficients in the bus voltage sampling module, reasonably setting the RC filter delay, and combining the set hardware hysteresis control module. Hardware automatic control is realized during the power-on and power-off process, saving DSP port resources, and at the same time improving the PCB layout, placing the control loop near the bus voltage sampling, shortening the wiring, and improving the anti-interference characteristics of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Shown is a structural principle diagram of the power-on surge suppression control circuit described in an embodiment of the present application.

[0018] Figure 2 Shown is a structural principle diagram of a power-on surge suppression control circuit according to another embodiment of the present application.

[0019] Figure 3 Shown is a circuit schematic diagram of a power-on surge suppression control circuit described in an embodiment of the present application.

[0020] Figure 4 Shown is a circuit diagram of the power-on surge suppression control described in an embodiment of the present application.

[0021] Figure 5 Shown is a schematic diagram of waveforms when the variable frequency drive according to an embodiment of the present application is powered on.

[0022] Figure 6 Shown is a schematic diagram of waveforms when the variable frequency drive described in an embodiment of the present application is powered off.

[0023] Figure 7 Shown is a principle flow chart of the power-on surge suppression control method described in an embodiment of the present application.

[0024] Component number description

[0025] 1 Power-on surge suppression control circuit of variable frequency drive

[0026] 11 Rectifier module

[0027] 12 Bus voltage sampling module

[0028] 121 First sampling unit

[0029] 122 Second sampling unit

[0030] 13 Hardware Hysteresis Control Module

[0031] 131 Hysteresis Comparator Unit

[0032] 132 Comparator Units

[0033] 14 Power-on surge control module

[0034] Steps S11 to S13 DETAILED DESCRIPTION

[0035] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0036] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present application in a schematic manner, and therefore the illustrations only show components related to the present application rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0037] In addition, in this application, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0038] PTC resistor is a thermistor sensor used for motor temperature monitoring and protection. PTC is a positive temperature coefficient thermistor, and its resistance increases with the increase of temperature. During the operation of the motor, if the temperature exceeds the set threshold value, the resistance of the PTC will increase sharply, in this way, it can be detected whether the motor is overheated.

[0039] In some solutions, by inserting a current-limiting PTC resistor in the front-end rectifier circuit, the electrolytic capacitor is slowly pre-charged, and then the software controls the relay to bypass the current-limiting resistor, so as to start the inverter to work normally. However, this control method requires the cooperation of software and hardware. First, the DSP chip needs to detect the input voltage in real time, and the bus voltage in real time. When the voltage difference of "peak value of input voltage - bus voltage" is less than a range (such as 20V-40V), the DSP controls the relay through an IO port to bypass the current-limiting PTC resistor and start the frequency converter. The current flows through the relay to prevent the current from being divided by the current-limiting resistor and causing abnormal operation of the back end. The entire function requires an input voltage detection circuit and a bus voltage detection circuit. DSP control requires 2 AD ports + 1 IO port, which occupies a certain degree of PCB layout and DSP resources. In some projects with tight DSP port resources, it may face the problem of replacing more pins of DSP. At the same time, the long-distance transmission of sampling signals and control signals also has potential anti-interference risks.

[0040] At least to address the above-mentioned problems, the present application provides a power-on surge suppression control circuit and method for a frequency converter. By setting two voltage sampling units with inconsistent sampling coefficients and reasonably setting the RC filter delay, combined with the set hardware hysteresis control module, a hardware implementation method for reliable and adaptive variable frequency drive PTC power-on surge suppression control is realized, and hardware automatic control is realized during the power-on and power-off process, thereby saving DSP port resources and improving PCB layout, placing the control loop near the bus voltage sampling, thereby further shortening the wiring and improving the anti-interference characteristics of the system.

[0041] The technical solutions in the embodiments of the present application will be described in detail below in conjunction with the drawings in the embodiments of the present application.

[0042] See also Figure 1 , which is a structural principle diagram of the power-on surge suppression control circuit of the variable frequency drive according to the embodiment of the present application. Figure 1 As shown, this embodiment provides a power-on surge suppression control circuit 1 for a variable frequency drive, which specifically includes: a rectifier module 11 , a bus voltage sampling module 12 , a hardware hysteresis control module 13 , and a power-on surge control module 14 .

[0043] In this embodiment, the rectifier module 11 provides a DC power supply; the bus voltage sampling module 12 is connected to the rectifier module 11, and is used to sample the bus voltage to obtain two DC bus voltage sampling values; the hardware hysteresis control module 13 is connected to the bus voltage sampling unit, and is used to receive the two DC bus voltage sampling values, and output a PTC control signal based on the two bus voltage values; the power-on surge control module 14 is respectively connected to the rectifier module 11 and the hardware hysteresis control module 13, and is used to receive the hysteresis control signal, and control the PTC resistor to be connected to or connected out of the rectifier module 11 based on the PTC control signal.

[0044] See also Figure 2 , which is a structural principle diagram of a power-on surge suppression control circuit of a variable frequency drive according to another embodiment of the present application.

[0045] like Figure 2 As shown, the bus voltage sampling module 12 includes: a first sampling unit 121 and a second sampling unit 122; wherein, the first sampling unit 121 and the second sampling unit 122 are commonly connected to the output end of the rectifier module 11; the first sampling unit 121 outputs the first DC bus voltage sampling value, and the second sampling unit 122 outputs the second bus voltage value.

[0046] like Figure 2 As shown, the hardware hysteresis control module 13 includes: a hysteresis comparison unit 131 and a comparator unit 132; wherein the hysteresis comparison unit 131 is connected to the bus voltage sampling module 12, for receiving the two bus voltage values, and outputting a hysteresis control signal based on the two bus voltage values; the comparator unit 132 is connected to the hysteresis comparison unit 131, for receiving the hysteresis control signal, and outputting a PTC control signal based on the hysteresis control signal.

[0047] See also Figure 3 , showing the circuit schematic diagram described in the embodiment of the present application.

[0048] like Figure 3 As shown, the rectifier module 11 includes: a bridge rectifier DN1, an energy storage capacitor E1, and a PTC resistor.

[0049] Among them, port 3 of the bridge rectifier DN1 is connected to the N-level of the AC power supply, port 2 is connected to one end of the PTC resistor, the other end of the PTC resistor is connected to the L-level of the AC power supply, port 1 of the bridge rectifier DN1 is connected to the positive electrode of the energy storage capacitor E1, and port 4 is connected to the negative electrode of the energy storage capacitor E1.

[0050] When the variable frequency drive is powered on, the rectifier module 11 converts the AC power into a DC power.

[0051] The bus voltage sampling module 12 includes: a first sampling unit 121 and a second sampling unit 122 .

[0052] The first sampling unit 121 includes: a first voltage-dividing resistor group: a voltage-dividing resistor R2, a voltage-dividing resistor R4, a voltage-dividing resistor R8, a voltage-dividing resistor R12, and a voltage-dividing resistor R9; a first operational amplifier U1A, and a first capacitor C2.

[0053] Specifically, the voltage-dividing resistor R2, the voltage-dividing resistor R4, the voltage-dividing resistor R8 and the voltage-dividing resistor R12 are connected in series in sequence, the other end of the voltage-dividing resistor R12 is connected to the positive electrode of the energy storage capacitor E1, the other end of the voltage-dividing resistor R12 is connected to the negative electrode of the energy storage capacitor E1, one end of the voltage-dividing resistor R9 is connected to the connecting line between the voltage-dividing resistor R8 and the voltage-dividing resistor R12, the other end of the voltage-dividing resistor R9 is connected to the positive input port No. 3 of the first operational amplifier U1A, the negative input port No. 2 of the first operational amplifier U1A is connected to the output port No. 1 of the first operational amplifier U1A, the positive input port No. 4 of the first operational amplifier U1A is grounded, the negative input port No. 8 of the first operational amplifier U1A is connected to the connecting line between one end of the first capacitor C2 and the switching power supply, and the other end of the first capacitor C2 is grounded.

[0054] It should be noted that the switching power supply in this embodiment is 3.3V.

[0055] The second sampling unit 122 includes: a second voltage-dividing resistor group: a voltage-dividing resistor R1 , a voltage-dividing resistor R3 , a voltage-dividing resistor R7 , and a voltage-dividing resistor R11 .

[0056] Specifically, the voltage dividing resistors R1, R3, R7 and R11 are connected in series in sequence, the other end of the voltage dividing resistor R1 is connected to the positive electrode of the energy storage capacitor E1, and the other end of the voltage dividing resistor R11 is connected to the negative electrode of the energy storage capacitor E1.

[0057] The hardware hysteresis control module 13 includes a hysteresis comparison unit 131 and a comparator unit 132 .

[0058] The hysteresis comparison unit 131 includes: a second operational amplifier U1B, a third resistor: a current limiting resistor R10, a fourth resistor: a current limiting resistor R13, a fifth resistor: a current limiting resistor R5, a sixth resistor: a positive feedback resistor R6 and a second capacitor C1.

[0059] Specifically, the positive input port No. 5 of the second operational amplifier U1B is respectively connected to one end of the current limiting resistor R10 and one end of the current limiting resistor R5, the other end of the current limiting resistor R10 is connected to the output port No. 1 of the first operational amplifier U1A, the other end of the current limiting resistor R5 is connected to the switching power supply 3.3V, one end of the positive feedback resistor R6 is connected to the positive input port No. 5 of the second operational amplifier U1B, and the other end is connected to the output port No. 7 of the second operational amplifier U1B, the negative input port No. 6 of the second operational amplifier U1B is respectively connected to one end of the current limiting resistor R13 and one end of the second capacitor C1, the other end of the current limiting resistor R13 is connected to the connecting line of the voltage divider resistor R7 and the voltage divider resistor R11, and the other end of the second capacitor C1 is grounded.

[0060] The positive input port 5 of the second operational amplifier U1B is connected to the first DC bus voltage sampling value of the first sampling unit 121, and the negative input of the second operational amplifier U1B is connected to the second DC bus voltage sampling value of the second sampling unit 122 through the RC filter composed of the current limiting resistor R13 and the second capacitor C1.

[0061] In this embodiment, the wide voltage working characteristic of the switching power supply is utilized. During the power-on process of the variable frequency drive, the switching power supply starts normally before the bus power provided by the bus. That is, during the power-on initialization stage of the variable frequency drive, the positive input port 5 of the second operational amplifier U1B preferentially introduces the bias voltage provided by the switching power supply 3.3V, so that the positive input is always higher than the negative input for a period of time before the bus is established. By introducing positive feedback and utilizing the characteristic of infinite switching gain, the voltage at the output port 7 of the second operational amplifier U1B is close to the switching voltage 3.3V for a period of time before the bus voltage is charged to the set value.

[0062] When the bus voltage is charged to the set value, the voltage of the negative input port 6 of the second operational amplifier U1B is higher than the voltage of the positive input port 5 of the second operational amplifier U1B, and under infinite gain, the output state of the output port 7 of the second operational amplifier U1B is lower than the bias power supply ground. Preferably, after the output voltage of the output port 7 of the second operational amplifier U1B is reverse biased to a low level, the input voltage of the positive input port 5 of the second operational amplifier U1B is reduced, and a voltage hysteresis difference is introduced to prevent the output state of the output port 7 of the second operational amplifier U1B from being unstable.

[0063] During the power-off process, the bus voltage gradually decreases, and the voltage of the negative input port 6 of the second operational amplifier U1B is again lower than the voltage of the positive input port 5 of the second operational amplifier U1B, thereby flipping the output port 7 of the second operational amplifier U1B to a high level of 3.3V. At the same time, the voltage of the positive input port 5 of the second operational amplifier U1B is raised, providing a hysteresis voltage, thereby keeping the output of the output port 7 of the second operational amplifier U1B at a high level.

[0064] The comparator unit 132 includes: a third operational amplifier U2A, a current limiting resistor R16, a voltage dividing resistor R17, a voltage dividing resistor R18, and a decoupling capacitor C3.

[0065] Specifically, the positive input port No. 3 of the third operational amplifier U2A is respectively connected to one end of the voltage-dividing resistor R17 and one end of the voltage-dividing resistor R18, the other end of the voltage-dividing resistor R17 is connected to the switching power supply 3.3V, and the other end of the voltage-dividing resistor R18 is grounded, the negative input port No. 2 of the third operational amplifier U2A is connected to one end of the current-limiting resistor R16, and the other end of the current-limiting resistor R16 is connected to the output port No. 7 of the second operational amplifier U1B, the negative input port No. 8 of the third operational amplifier U2A and one end of the decoupling capacitor C3 are commonly connected to the switching power supply 3.3V, and the other end of the decoupling capacitor C3 is grounded.

[0066] In this embodiment, within a period of time before the bus voltage is charged to the set value, the threshold voltage of the positive input port 3 of the third operational amplifier U2A is made smaller than the negative input port 2 of the third operational amplifier U2A through the voltage-dividing resistors R17 and R18, so that the PTC control signal output by the comparator unit 132 to the power-on surge control module 14 remains in a low level state.

[0067] When the bus voltage is charged to the set value, the input voltage of the negative input port 2 of the third operational amplifier U2A decreases and is less than the threshold voltage of the positive input port 3 of the third operational amplifier U2A, so that the PTC control signal output by the comparator unit 132 to the power-on surge control module 14 is flipped to a high level state.

[0068] During the power-off process, since the output port 7 of the second operational amplifier U1B is converted to a high-level 3.3V output, the input voltage of the negative input port 2 of the third operational amplifier U2A is greater than the threshold voltage of the positive input port 3 of the third operational amplifier U2A, thereby causing the PTC control signal output by the comparator unit 132 to the power-on surge control module 14 to flip to a low-level state.

[0069] The power-on surge control module 14 includes: a relay RY1 , an N-type transistor Q1 , a resistor R14 , a resistor R15 , and a diode D1 .

[0070] Among them, the base of the N-type tube Q1 is respectively connected to one end of the resistor R14 and one end of the resistor R15, the other end of the resistor R14 is connected to the output end of the hardware hysteresis control module 13, the other end of the resistor R15 and the emitter of the N-type tube Q1 are grounded together, the collector of the N-type tube Q1 is connected to one end of the relay RY1, the other end of the relay RY1 is connected to the power supply 12V, and the relay RY1 is connected to the two ends of the PTC resistor of the rectifier module 11.

[0071] In a period of time before the bus voltage is charged to the set value, the power-on surge control module 14 receives the low-level PTC control signal output by the hardware hysteresis control module 13, keeps the switch of the relay RY1 open, and keeps the PTC resistor connected to the circuit.

[0072] When the bus voltage is charged to the set value, the power-on surge control module 14 receives the PTC control signal output by the hardware hysteresis control module 13 and flips to a high level state, so that the switch of the relay RY1 is energized, thereby bypassing the PTC resistor and allowing the variable frequency drive to enter a normal working state.

[0073] During the power-off process, the power-on surge control module 14 receives the low-level PTC control signal output by the hardware hysteresis control module 13, disconnects the switch of the relay RY1, connects the PTC resistor to the circuit again, and prepares for the next power-on of the variable frequency drive.

[0074] See also Figure 4 , which is a circuit schematic diagram of the power-on surge suppression control circuit described in an embodiment of the present application. Figure 4 The connection relationship of the circuit schematic diagram shown in Figure 3 The same, so no further elaboration is given here.

[0075] like Figure 4 As shown, the input voltage of the input end of the rectifier module 11 is 220VAC, and the energy storage capacitor in the rectifier module 11 is 680Uf; the resistors for sampling in the first sampling unit 121 in the bus voltage sampling module 12 include: resistor R6, resistor R7, resistor R8, resistor R9, resistor R10, and the resistors for sampling in the second sampling unit 122 include: resistor R1, resistor R2, resistor R3, resistor R4, resistor R5; the RC filter composed of resistor R21 and capacitor C2 is used to input the second DC bus voltage sampling value output by the second sampling unit 122 to the hysteresis comparison unit 131. The values ​​of each circuit element can be found in Figure 4 .

[0076] In this embodiment, the power-on surge suppression control circuit of the entire variable frequency drive does not need to be connected to the DSP controller, and the DSP controller is not required to perform AD sampling on the input voltage and bus voltage. At the same time, there is no need for the DSP controller to control the output PTC control signal, saving 3 DSP port resources. At the same time, by simply adjusting the parameters, it can adapt to the application of different bus energy storage capacitor values ​​and different input voltage ranges; the entire added loop is concentrated on the energy storage filter side, and it also has better tolerance for layout and routing, thereby improving the anti-interference characteristics of the system.

[0077] See also Figure 5 , which is a schematic diagram of the waveform when the variable frequency drive described in the embodiment of the present application is powered on.

[0078] like Figure 4 and Figure 5 As shown, the first sampling unit 121 outputs the first DC bus voltage sampling value to the positive input terminal of the second operational amplifier (hysteresis comparator) U3B through the first operational amplifier (op amp follower) U3A, and the second sampling unit 122 outputs the second DC bus voltage sampling value directly to the negative input terminal of the second operational amplifier (hysteresis comparator) U3B through RC filtering.

[0079] When the bus voltage is very low (assuming the bus voltage is 0V at this time), the positive input terminal of the second operational amplifier (hysteresis comparator) U3B introduces resistor R22 connected to the switching power supply 3.3V, and the negative feedback has no resistor, making the loop gain infinite, so that the positive input voltage of the second operational amplifier (hysteresis comparator) U3B (calculated to be 1.8V) is greater than the negative input voltage of the second operational amplifier (hysteresis comparator) U3B, and the output terminal of the second operational amplifier (hysteresis comparator) U3B is forward biased to the switching power supply 3.3V.

[0080] In the period before the bus voltage is charged to the set value, the output end of the second operational amplifier (hysteresis comparator) U3B is always at a high level of 3.3V, which is greater than the threshold voltage set at the positive input end of the third operational amplifier U2A, and the output level of the third operational amplifier U2A is 0, that is, the PTC control signal output by the third operational amplifier U2A is a PTC low-level control signal, thereby keeping the relay in the disconnected state. Preferably, the threshold voltage set at the positive input end of the third operational amplifier U2A is set to 1.65V.

[0081] When the bus voltage is charged to the set value, the input voltage of the positive input terminal of the second operational amplifier (hysteresis comparator) U3B is equal to the input voltage of the negative input terminal. When the bus voltage charge continues to increase, the input voltage of the positive input terminal of the second operational amplifier (hysteresis comparator) U3B is less than the input voltage of the negative input terminal, so that the output of the output port of the second operational amplifier (hysteresis comparator) U3B is reverse biased to 0V, which is less than the threshold voltage set at the positive input terminal of the third operational amplifier U2A. Then the output level of the third operational amplifier U2A is 1, that is, the PTC control signal output by the third operational amplifier U2A is a PTC high-level control signal, so that the relay becomes the energized state, thereby bypassing the PTC resistor. Preferably, the set value of the bus voltage is 268V.

[0082] Figure 5 In the figure, channel A represents the waveform of the bus voltage, and channel B represents the waveform of the relay control signal (the waveform of the PTC control signal output by the third operational amplifier U2A). When the bus voltage is close to 270V, the relay control signal flips to a high level, realizing bypass control of the PTC resistor. The charging time is about 1s. At this time, the voltage difference of the bus voltage is only about 40V, and the impact current is greatly reduced.

[0083] See also Figure 6 , which is a schematic diagram of the waveform when the variable frequency drive described in the embodiment of the present application is powered off.

[0084] Combination Figure 4 and Figure 6 When the power is off, the bus voltage drops, and the voltage of the negative input of the second operational amplifier (hysteresis comparator) U3B is lower than the positive input voltage of the second operational amplifier (hysteresis comparator) U3B again, so that the output of the second operational amplifier (hysteresis comparator) U3B is flipped to a high level of 3.3V, and at the same time, the positive input voltage of the second operational amplifier (hysteresis comparator) U3B is raised, providing a hysteresis voltage, so that the output is kept at a high level. Since the output of the second operational amplifier (hysteresis comparator) U3B is converted to a high level 3.3V output, the input voltage of the negative input of the third operational amplifier U2A is greater than the threshold voltage of the positive input, so that the output PTC control signal is flipped to a low level state (PTC low level control signal), so that the relay switch is disconnected, allowing the PTC resistor to be connected to the circuit again, and preparing for the next power-on of the variable frequency drive.

[0085] Figure 6In the figure, channel A represents the waveform of the bus voltage, and channel B represents the waveform of the relay control signal (the waveform of the PTC control signal output by the third operational amplifier U2A). When the bus voltage drops to about 210V, it reaches the window flip limit of the second operational amplifier (hysteresis comparator) U3B, and the relay control signal flips to a low level, and the PTC resistor is cut into the circuit again to inhibit the start-up of the impact current when the frequency converter is powered on next time. At this time, the voltage difference of the bus voltage is about 60V, which prevents false triggering caused by power supply ripple fluctuations and ensures reliable control.

[0086] See also Figure 7 , which is a principle flow chart of the power-on surge suppression control method of the variable frequency drive according to the embodiment of the present application. Figure 7 As shown, this embodiment provides a power-on surge suppression control method for a variable frequency drive, which specifically includes the following steps:

[0087] S11, sampling the bus voltage, and obtaining a first DC bus voltage sampling value and a second DC bus voltage sampling value.

[0088] S12: output a PTC control signal based on the first DC bus voltage sampling value and the second DC bus voltage sampling value.

[0089] S13, controlling the PTC resistor to be connected to or connected out of the control circuit according to the PTC control signal.

[0090] The protection scope of the power-on surge suppression control method of the variable frequency drive described in the embodiment of the present application is not limited to the execution order of the steps listed in the present embodiment. All solutions implemented by adding, reducing or replacing steps in the prior art based on the principles of the present application are included in the protection scope of the present application.

[0091] The power-on surge suppression control circuit of the variable frequency drive described in the embodiment of the present application can implement the power-on surge suppression control method of the variable frequency drive described in the present application, but the implementation device of the power-on surge suppression control method of the variable frequency drive described in the present application includes but is not limited to the structure of the power-on surge suppression control circuit of the variable frequency drive listed in the present embodiment. All structural deformations and replacements of the prior art made according to the principles of the present application are included in the protection scope of the present application.

[0092] In the several embodiments provided in the present application, it should be understood that the disclosed circuits, power supply devices or methods can be implemented in other ways. For example, the power supply device embodiments described above are only schematic, for example, the division of modules / units is only a logical function division, and there may be other division methods in actual implementation, for example, multiple modules or units can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or modules or units, which can be electrical, mechanical or other forms.

[0093] Those of ordinary skill in the art should further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0094] The descriptions of the processes or structures corresponding to the above-mentioned figures have different emphases. For parts that are not described in detail in a certain process or structure, please refer to the relevant descriptions of other processes or structures.

[0095] The above embodiments are merely illustrative of the principles and effects of the present application and are not intended to limit the present application. Anyone familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed in the present application shall still be covered by the claims of the present application.

Claims

1. A power-on surge suppression control circuit for a variable frequency drive, characterized in that: The control circuit includes: a rectifier module, a bus voltage sampling module, a hardware hysteresis control module and a power-on surge control module; wherein, The rectifier module provides a DC power supply; The bus voltage sampling module is connected to the rectifier module and is used to sample the bus voltage to obtain two DC bus voltage sampling values; The hardware hysteresis control module is connected to the bus voltage sampling unit, and is used to receive the two DC bus voltage sampling values, and output a PTC control signal based on the two bus voltage values; The power-on surge control module is connected to the rectifier module and the hardware hysteresis control module respectively, and is used to receive the hysteresis control signal and control the PTC resistor to be connected to or connected out of the rectifier module based on the PTC control signal.

2. The power-on surge suppression control circuit of the variable frequency drive according to claim 1, characterized in that: The bus voltage sampling module includes: a first sampling unit and a second sampling unit; wherein, The first sampling unit and the second sampling unit are commonly connected to the output end of the rectifier module; the first sampling unit outputs a first DC bus voltage sampling value, and the second sampling unit outputs a second bus voltage value.

3. The power-on surge suppression control circuit of the variable frequency drive according to claim 2, characterized in that: The first sampling unit includes: a first voltage-dividing resistor group, a first operational amplifier, and a first capacitor; One end of the first voltage-dividing resistor group is connected to the positive output of the rectifier module, and the other end is connected to the negative output of the rectifier module; The positive input terminal of the first operational amplifier is connected to the first voltage-dividing resistor group, the negative input terminal of the first operational amplifier is connected between one end of the first capacitor and a switching power supply, the negative input terminal of the first operational amplifier is also connected to the output terminal of the first operational amplifier, and the input terminal of the first operational amplifier and the other end of the first capacitor are grounded.

4. The power-on surge suppression control circuit of the variable frequency drive according to claim 2, characterized in that: The second sampling unit includes: a second voltage-dividing resistor group; one end of the second voltage-dividing resistor group is connected to the positive output of the rectifier module, and the other end is connected to the negative output of the rectifier module.

5. The power-on surge suppression control circuit of the variable frequency drive according to claim 1, characterized in that: The hardware hysteresis control module includes: a hysteresis comparison unit and a comparator unit; wherein, The hysteresis comparison unit is connected to the bus voltage sampling module, and is used to receive the two bus voltage values, and output a hysteresis control signal based on the two bus voltage values; The comparator unit is connected to the hysteresis comparison unit, and is configured to receive the hysteresis control signal and output a PTC control signal based on the hysteresis control signal.

6. The power-on surge suppression control circuit of the variable frequency drive according to claim 5, characterized in that: The hysteresis comparison unit includes: a second operational amplifier, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor and a second capacitor; One end of the third resistor is connected to the first DC bus voltage sampling value output by the bus voltage sampling module, and the other end is connected to the positive input terminal of the second operational amplifier; one end of the fourth resistor is connected to the second DC bus voltage sampling value output by the bus voltage sampling module, and the other end is connected to the negative input terminal of the second operational amplifier; One end of the fifth resistor is connected to one end of the sixth resistor, the other end of the fifth resistor is connected to a switching power supply, and the other end of the sixth resistor is connected to the output end of the second operational amplifier; The positive input terminal of the second operational amplifier is also connected to the connection line between one end of the fifth resistor and the other end of the sixth resistor, the negative input terminal of the second operational amplifier is also connected to one end of the second capacitor, and the other end of the second capacitor is grounded.

7. The power-on surge suppression control circuit of the variable frequency drive according to claim 5, characterized in that: The comparator unit includes: a third operational amplifier, a seventh resistor, an eighth resistor, a ninth resistor and a third capacitor; One end of the seventh resistor is connected to the output end of the hysteresis comparison unit, and the other end is connected to the negative input end of the third operational amplifier; one end of the eighth resistor is connected to the switching power supply, and the other end is connected to one end of the ninth resistor; and the other end of the ninth resistor is grounded; The positive input terminal of the third operational amplifier is connected to the connecting line between the other end of the eighth resistor and one end of the ninth resistor, the negative input terminal of the third operational amplifier and one end of the third capacitor are commonly connected to the switching power supply, the other end of the third capacitor is grounded, and the output terminal of the third operational amplifier is connected to the power-on surge control module.

8. The power-on surge suppression control circuit of the variable frequency drive according to claim 1, characterized in that: The power-on surge control module includes a relay, and the rectifier module includes a PTC resistor; The two ends of the switch of the relay are respectively connected to the two ends of the PTC resistor, and the input end of the relay receives the PTC control signal output by the hardware hysteresis control module to control the closing or opening of the switch of the relay.

9. The power-on surge suppression control circuit of the variable frequency drive according to claim 8, characterized in that: The PTC control signal includes: a PTC high level control signal and a PTC low level control signal; The power-on surge control module controls the relay to be attracted based on the PTC high-level control signal, so that the PTC resistor is connected out of the rectifier module; The power-on surge control module controls the relay to be disconnected based on the PTC low-level control signal, so that the PTC resistor is connected to the rectifier module.

10. A method for controlling power-on surge suppression of a variable frequency drive, characterized in that: The control method comprises: Sampling the bus voltage, and obtaining a first DC bus voltage sampling value and a second DC bus voltage sampling value; Outputting a PTC control signal based on the first DC bus voltage sampling value and the second DC bus voltage sampling value; The PTC resistor is controlled to be connected to or connected out of the control circuit according to the PTC control signal.

Images