Motor control system and air conditioner

Abstract

The invention discloses a motor control system and an air conditioner, and the system comprises a voltage release circuit which comprises a voltage-regulator tube and a resistor which are connected in series; the voltage acquisition module is used for acquiring bus voltage; the control unit is configured to execute the following steps when receiving a motor braking instruction: repeatedly and simultaneously controlling the on-off of three switch tubes in three lower bridge arms in the IPM module, and after the bus voltage is raised to the action voltage of the voltage-regulator tube, the raised voltage is consumed through a resistor; when the bus voltage is boosted, the bus voltage is monitored in real time, and when the bus voltage is boosted to reach the threshold voltage, the duty ratio of the same PWM signal sent to the three switching tubes at the same time is reduced. According to the invention, the purpose of rapid braking of the motor can be realized through the voltage release circuit and by controlling the on-off of three switch tubes in three lower bridge arms in the IPM module, and meanwhile, the bus voltage is prevented from being increased too high.

Description

Technical Field

[0001] The present invention relates to the technical field of fan control, and particularly to a motor control system and an air conditioner. Background Art

[0002] As an important component of an air conditioner, a permanent magnet synchronous fan motor is used in both the indoor unit and the outdoor unit, and the fan motor adopts a permanent magnet synchronous motor (PMSM).

[0003] In the motor control scheme, there are some application scenarios that require a significant reduction in the motor speed within a short period of time. Currently, there are two solutions: the first is to equip the motor with a set of mechanical braking devices, which will increase the cost and cause mechanical wear; the second is to convert the kinetic energy of the motor into electrical energy during braking, raise the bus voltage, and forcibly perform energy consumption braking on the fan through a braking circuit to consume this part of the voltage, thereby achieving the purpose of reducing the motor speed.

[0004] For a common braking circuit, see Figure 2 , which is connected in parallel to the DC bus and includes a switching tube K1 and a resistor R1. When the braking energy of the motor is recharged to the DC bus and rises to a certain value, the switching tube K1 is turned on, and the energy is consumed in the resistor R1. When the bus voltage is lower than a certain value, the switching tube K1 is turned off, and the normal operation is entered.

[0005] The advantages of this scheme are that it can quickly brake by consuming energy, but there are two disadvantages: First, the motor speed cannot be controlled during the motor deceleration process; Second, when the motor speed decreases and the back electromotive force is lower than the bus voltage, there is no current path at this time, and the kinetic energy of the motor cannot be converted into electrical energy. Therefore, the motor cannot raise the bus voltage by self-rotation. Even if the switching tube K1 is closed, the motor cannot be decelerated, and at this time, the braking circuit cannot play a role. Therefore, the power supply needs to be cut off before the motor braking, and the back electromotive force generated by the motor self-rotation can also be reversely charged to the bus through the freewheeling diode in the IPM module. Only when the switching tube K1 is closed at this time will the braking effect be achieved.

[0006] The above information disclosed in this background art is only used to increase the understanding of the background art of the present application. Therefore, it may include prior art that is not known to those of ordinary skill in the art. Summary of the Invention

[0007] In view of the problems pointed out in the background art, the present application provides a motor control system. By connecting a pressure relief circuit formed by a voltage regulator tube and a resistor in parallel to the bus, and controlling the on-off of three switching tubes in the three lower bridge arms of the IPM module, the purpose of quickly braking the motor is achieved, and at the same time, the excessive rise of the bus voltage is avoided.

[0008] To achieve the above-mentioned invention objectives, the present invention is implemented by the following technical solutions: This application relates to a motor control system, including: A rectification unit, which is used to rectify three-phase alternating current into direct current; A PFC circuit, which is connected between the output terminal of the rectification unit and the electrolytic capacitor, and is used for power factor correction of the power supply. The electrolytic capacitor outputs a stable bus DC power supply; An IPM module, which is used to invert the bus DC power supply into three-phase voltage to supply power to the motor; A pressure relief circuit, which is connected in parallel to the bus and is located at the front end of the IPM module. The pressure relief circuit includes a series-connected voltage regulator tube and a resistor; A voltage acquisition module, which is used to acquire the bus voltage; A control unit, which is configured to perform the following when receiving a motor braking instruction: Repeatedly and simultaneously control the opening and closing of three switching tubes in three lower bridge arms of the IPM module. After the bus voltage rises to reach the operating voltage of the voltage regulator tube, the lifted voltage is consumed by the resistor; While lifting the bus voltage, monitor the bus voltage in real time. When the bus voltage rises beyond the threshold voltage, reduce the duty cycle of the same PWM signal sent to the three switching tubes simultaneously; Among them, the same PWM signal is sent to the three switching tubes in the three lower bridge arms simultaneously to make the three switching tubes connected; The stable bus voltage, the operating voltage of the voltage regulator tube, and the threshold voltage increase in sequence.

[0009] The motor control system involved in this application has a pressure relief circuit connected in parallel to the bus. The voltage regulator tube in the pressure relief circuit is a passive device, which reduces the cost.

[0010] By controlling the simultaneous opening and closing of three switching tubes in three lower bridge arms, even when the back electromotive force of the motor is lower than the bus voltage, the electrolytic capacitor can be charged and the bus voltage can be lifted. When the lifted voltage reaches the operating voltage of the voltage regulator tube, the voltage regulator tube conducts and the voltage will also be released through the pressure relief circuit to achieve the purpose of decelerating the motor. This method does not require cutting off the power supply before braking, reduces the system operation complexity, and also increases the operation reliability.

[0011] In some embodiments of this application, the motor control system further includes: A rotation speed detection unit, which is used to detect the rotation speed of the motor during braking; The control unit is further configured to: Judge whether the target rotation speed of the motor is zero. If so, proceed to S1; if not, proceed to S2; S1: Repeatedly and simultaneously control the on-off of the three switching transistors in the three lower bridge arms of the IPM module until the motor stops. Among them, send the same PWM signal with the first duty cycle to the three switching transistors in the three lower bridge arms at the same time to connect the three switching transistors; S2: Repeatedly and simultaneously control the on-off of the three switching transistors in the three lower bridge arms of the IPM module. Among them, send the same PWM signal with the first duty cycle to the three switching transistors in the three lower bridge arms at the same time to connect the three switching transistors; During the process of reducing the motor speed, continuously judge whether the motor speed is close to the target speed. If so, reduce the duty cycle of the same PWM signal sent to the three switching transistors in the three lower bridge arms at the same time until the speed reaches the target speed. If not, return to S2; After the speed reaches the target speed, switch back to the normal drive control of the motor.

[0012] For the motor control system involved in this application, when the target speed is 0, a larger duty cycle of the PWM signal is adopted to rapidly increase the bus voltage and rapidly reduce the motor speed. And an active voltage stabilizing tube device is adopted to automatically release the increased bus voltage.

[0013] When the target speed is not zero, when the speed is close to the target speed, control to reduce the duty cycle of the same PMW signal sent to the three switching transistors in the three lower bridge arms, reduce the rising speed of the bus voltage, and thus also reduce the speed reduction rate of the motor to achieve speed closed-loop control.

[0014] In some embodiments of this application, the speed detection unit includes voltage dividing resistors connected in parallel to each of at least two of the three switching transistors in the three lower bridge arms.

[0015] Through the divided voltages sampled by the first voltage dividing resistor and the second voltage dividing resistor respectively, the control unit calculates and obtains the self-rotation speed of the motor, which is convenient for realizing speed closed-loop control during motor braking.

[0016] In some embodiments of this application, the control unit is further configured to: While increasing the bus voltage, also continuously monitor the voltage rising rate of the bus voltage; When the voltage rising rate reaches the preset threshold, output an alarm reminder.

[0017] When judging whether the bus voltage reaches the threshold voltage, the response should be fast. Otherwise, too high a voltage will be formed across the electrolytic capacitor and breakdown will occur. Therefore, to avoid this situation, the rising trend of the bus voltage can be judged by monitoring the voltage rising rate of the bus voltage, and when outputting the alarm reminder, the bus voltage can be controlled to drop in advance to prevent damage to the electrolytic capacitor caused by the bus voltage reaching the threshold voltage.

[0018] In some embodiments of the present application, the voltage acquisition module includes a plurality of voltage dividing resistors connected in series between the positive and negative poles of the bus DC power supply.

[0019] The plurality of voltage dividing resistors are used to detect the bus voltage, facilitating the control of the rising speed of the bus voltage.

[0020] In some embodiments of the present application, the frequency of the PWM signal is consistent with the motor drive frequency. For example, a frequency of 7KHz can be adopted.

[0021] The present application also relates to an air conditioner, including: A refrigerant circulation loop that circulates refrigerant in a loop composed of a compressor, a condenser, an expansion valve, and an evaporator; A compressor for compressing low-temperature and low-pressure refrigerant gas into high-temperature and high-pressure refrigerant gas and discharging it to the condenser; An outdoor heat exchanger and an indoor heat exchanger, where one operates as a condenser and the other operates as an evaporator; A variable-frequency topology circuit structure, including a rectification unit, a PFC circuit, and an IPM module. The rectification unit is used to rectify three-phase alternating current into direct current. The PFC circuit is connected between the output end of the rectification unit and an electrolytic capacitor for power factor correction of the power supply. The electrolytic capacitor outputs a stable bus DC power supply. The IPM module is used to invert the bus DC power supply into three-phase voltage to supply power to a motor, and the motor is a compressor motor, an outdoor fan motor for heat exchange of the outdoor heat exchanger, or an indoor fan motor for heat exchange of the indoor heat exchanger; A pressure relief circuit, which is connected in parallel to the bus and is located at the front end of the IPM module. The pressure relief circuit includes a zener diode and a resistor connected in series; A voltage acquisition module for acquiring the bus voltage; A control unit configured to perform the following when receiving a motor braking instruction: Repeatedly and simultaneously control the opening and closing of three switching tubes in three lower bridge arms of the IPM module. After the bus voltage rises to reach the operating voltage of the zener diode, the elevated voltage is consumed through the resistor; While raising the bus voltage, monitor the bus voltage in real time. When the bus voltage rises beyond the threshold voltage, reduce the duty cycle of the same PWM signal simultaneously sent to the three switching tubes; Among them, the same PWM signal is simultaneously sent to three switching tubes in the three lower bridge arms to connect the three switching tubes; The stable bus voltage, the operating voltage of the zener diode, and the threshold voltage increase in sequence.

[0022] The air conditioner related to the present application, the motor control system as described above is applied to the motor for the compressor of the air conditioner and / or the motor for the outdoor fan and / or the motor for the indoor fan. Therefore, the air conditioner also has the advantages of the motor control system as described above.

[0023] When the motor of the air conditioner brakes, it can effectively achieve motor braking while ensuring the operation reliability of the variable-frequency topology circuit structure, thereby improving the operation reliability of the air conditioner.

[0024] In some embodiments of the present application, the air conditioner further includes: A rotational speed detection unit, which is used to detect the rotational speed of the motor during motor braking; The control unit is further configured to: Judge whether the target rotational speed of the motor is zero. If so, proceed to S1; if not, proceed to S2; S1: Repeatedly and simultaneously control the on-off of the three switching tubes in the three lower bridge arms of the IPM module until the motor stops. Among them, send the same PWM signal with a first duty cycle to the three switching tubes in the three lower bridge arms at the same time to make the three switching tubes connected; S2: Repeatedly and simultaneously control the on-off of the three switching tubes in the three lower bridge arms of the IPM module. Among them, send the same PWM signal with a first duty cycle to the three switching tubes in the three lower bridge arms at the same time to make the three switching tubes connected; During the process of reducing the rotational speed of the motor, judge in real time whether the rotational speed of the motor is close to the target rotational speed. If so, reduce the duty cycle of the same PWM signal sent to the three switching tubes in the three lower bridge arms at the same time until the rotational speed reaches the target rotational speed. If not, return to S2; After the rotational speed reaches the target rotational speed, switch back to the normal drive control of the motor.

[0025] In some embodiments of the present application, the rotational speed detection unit includes voltage-dividing resistors connected in parallel to each of at least two of the three switching tubes in the three lower bridge arms.

[0026] In some embodiments of the present application, the control unit is further configured to: While boosting the bus voltage, it will also monitor the voltage rise rate of the bus voltage in real time; When the voltage rise rate reaches a preset threshold, output an alarm reminder.

[0027] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become clearer. Description of the Drawings

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 is the principle block diagram of an existing air conditioner; Figure 2 is the circuit diagram of a variable-frequency topology circuit structure for a PMSM; Figure 3 is the circuit diagram of the IPM module of a PMSM; Figure 4 is the circuit diagram of a braking circuit used in an existing variable-frequency topology circuit structure for a PMSM; Figure 5 is the circuit diagram of a pressure relief circuit used in a variable-frequency topology circuit structure for a PMSM in the motor control system proposed in this application; Figure 6 is the circuit of a speed detection unit used in a variable-frequency topology circuit structure for a PMSM in the motor control system proposed in this application Figure 1 ; Figure 7 is the circuit of a speed detection unit used in a variable-frequency topology circuit structure for a PMSM in the motor control system proposed in this application Figure 2 ; Figure 8 is the flowchart of the motor control system proposed in this application during motor braking; Figure 9 is the flowchart of the motor control system proposed in this application for judging the bus voltage during motor braking; Figure 10 is the flowchart of the motor control system proposed in this application for monitoring the voltage rise rate of the bus voltage during motor braking.

[0030] Reference numerals: 10, PMSM; 20, IPM module; 30, rectification unit; 40, PFC circuit; 50, pressure relief circuit; 60, voltage acquisition module. Detailed embodiments

[0031] The following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of them. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of this application.

[0032] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present application.

[0033] The terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0034] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected" and "coupled" shall be construed broadly. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0035] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely means that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely means that the horizontal height of the first feature is lower than that of the second feature.

[0036] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. This repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0037] [Basic working principle of air conditioner] See Figure 1 , the air conditioner performs a refrigeration cycle of the air conditioner by using a compressor, a condenser, an expansion valve, and an evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat the indoor space.

[0038] The low-temperature and low-pressure refrigerant enters the compressor, and the compressor compresses it into a refrigerant gas in a high-temperature and high-pressure state and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and heat is released to the surrounding environment through the condensation process.

[0039] The expansion valve expands the high-temperature and high-pressure liquid-phase refrigerant formed by condensation in the condenser into a low-pressure liquid-phase refrigerant. The evaporator evaporates the refrigerant expanded in the expansion valve and returns the refrigerant gas in a low-temperature and low-pressure state to the compressor. The evaporator can achieve a refrigeration effect by using the latent heat of evaporation of the refrigerant to exchange heat with the material to be cooled. Throughout the cycle, the air conditioner can adjust the temperature of the indoor space.

[0040] The outdoor unit of the air conditioner refers to the part of the refrigeration cycle including the compressor and the outdoor heat exchanger. The indoor unit of the air conditioner includes the indoor heat exchanger, and the expansion valve can be provided in the indoor unit or the outdoor unit.

[0041] The indoor heat exchanger and the outdoor heat exchanger are used as condensers or evaporators. When the indoor heat exchanger is used as a condenser, the air conditioner serves as a heater in the heating mode. When the indoor heat exchanger is used as an evaporator, the air conditioner serves as a cooler in the cooling mode.

[0042] The motor for the compressor, the motor for the outdoor fan, or the motor for the indoor fan is generally a permanent magnet synchronous motor (PMSM).

[0043] In the motor control system of a motor, it mainly involves an IPM (Intelligent Power Module) 20, a rectifier unit 30, a PFC circuit 40, a pressure relief circuit 50, a voltage acquisition module 60, and a control unit (not shown).

[0044] Using the IPM module 20 to perform variable frequency control on the PMSM 10 is a conventional technical means in variable frequency control, and will not be introduced in detail in this article.

[0045] See Figure 2 , in some embodiments of the present application, the power supply device of the motor may include a rectifier unit 30.

[0046] The input end of the rectifier unit 30 is connected to the AC power supply AC, and the rectifier unit 30 is used to rectify the alternating current provided by the AC power supply AC to obtain rectified direct current.

[0047] The rectifier unit 30 may be a bridge rectifier composed of four diodes.

[0048] In some embodiments of the present application, the power supply device of the motor may further include a PFC circuit 40 and an electrolytic capacitor E1.

[0049] The PFC circuit 40 is connected between the output end of the rectifier unit 30 and the electrolytic capacitor E1, and the PFC circuit 40 is used to perform power factor correction on the power supply.

[0050] The electrolytic capacitor E1 is connected in parallel with the load, where the load may refer to the PMSM 10, and the IPM module 20 is used to perform variable frequency control on the PMSM 10.

[0051] That is, after the AC power supply AC passes through the uncontrolled full-wave rectification of the rectifier unit 30, it then passes through the PFC circuit 40, and the output is connected to the large-capacity electrolytic capacitor E1, and then supplies power to the load.

[0052] It should be noted that the PFC circuit 40 may adopt a boost topology structure for boosting, and of course, a PFC circuit without a boosting function may also be used.

[0053] See Figure 2 , which shows the structure of the PFC circuit 40.

[0054] The rectifier unit 30 has a positive DC side and a negative DC side.

[0055] The PFC circuit 40 includes an inductor L1, a switching transistor IGBT Q1, and a diode D1.

[0056] One end of the positive DC side of the rectifier unit 30 is connected to one end of the inductor L1, and the other end of the inductor L1 is divided into two paths.

[0057] One path is connected to the collector of the switching transistor Q1, and the other path is connected to the anode of the diode D1.

[0058] The cathode of the diode D1 is the output terminal of the PFC circuit 40, and the electrolytic capacitor E1 is connected between the cathode of the diode D1 and the ground.

[0059] The working principle of the PFC circuit 40 is as follows: The inductor L1 stores energy when the switching transistor Q1 is turned on, and releases the stored energy to charge the large-capacity electrolytic capacitor E1 through the diode D1 when the switching transistor Q1 is turned off. The electrolytic capacitor E1 can output a smoothed and stabilized bus voltage Vdc.

[0060] Both the rectifying unit 30 and the electrolytic capacitor E1 are used in cooperation with the PFC circuit 40.

[0061] The PFC circuit 40 can not only correct the power factor of the power supply, but also boost the rectified direct current to provide a stable DC voltage for the electrolytic capacitor E1.

[0062] See Figure 3 , which shows the circuit diagram of the IPM module 20.

[0063] The IPM module 20 includes a three-phase power IPM module for inverting the DC power Vdc on the bus to drive the PMSM10.

[0064] The three-phase power IPM module consists of six power switching elements, namely, the power switching element T1 of the upper arm of the U phase, the power switching element T3 of the upper arm of the V phase, the power switching element T5 of the upper arm of the W phase, the power switching element T2 of the lower arm of the U phase, the power switching element T4 of the lower arm of the V phase, and the power switching element T6 of the lower arm of the W phase.

[0065] The structure and working principle of the three-phase power IPM module are well-known and will not be elaborated here.

[0066] The three-phase voltages UA, UB, and UC inverted and output by the three-phase power IPM module act on the PMSM 10.

[0067] The main control algorithm for the PMSM 10 is Field-Oriented Control (FOC), also known as vector control.

[0068] This FOC control is to perform inversion control on the IPM module 20, and the IPM module 20 inverts the DC power Vdc on the bus into an alternating current to supply the PMSM 10.

[0069] The FOC control is the normal drive control for the motor.

[0070] In the braking control of a permanent magnet synchronous motor, the rotor of the motor is a permanent magnet. When the motor brakes and rotates on its own, it is equivalent to the stator winding cutting the magnetic induction line, generating an induced electromotive force. At this time, the kinetic energy of the motor is converted into electrical energy (i.e., power generation), and the electromotive force voltage is proportional to the rotation speed of self-rotation.

[0071] In the existing motor control, the generated induced electromotive force will charge the bus, raising the bus voltage. In order to avoid damage to the electrolytic capacitor E1 due to excessive bus voltage, a braking circuit is configured to release the elevated voltage.

[0072] See Figure 4 , a braking circuit is connected in parallel to the bus. This braking circuit includes a series-connected switching tube K1 and a resistor R1.

[0073] When the motor speed is low, the induced electromotive force is lower than the bus voltage. At this time, there is no current path, and the kinetic energy cannot be converted into electrical energy, that is, it cannot charge the electrolytic capacitor E1.

[0074] When the motor speed is high, the induced electromotive force is higher than the bus voltage. Taking the U phase and V phase as examples for illustration.

[0075] At this time, the current direction is: U-phase winding → body diode of switching tube T1 → positive pole of the bus DC power supply → electrolytic capacitor E1 → negative pole of the bus DC power supply → body diode of switching tube T4 → V-phase winding. In this way, the bus voltage rises, the electrical energy is converted from the rotational kinetic energy into electrical energy, and the motor speed decreases.

[0076] Therefore, when the induced electromotive force of the motor is lower than the bus voltage, even if the switching tube K1 is turned on, the motor cannot be decelerated, and at this time the braking circuit cannot function. Therefore, before braking, the power supply needs to be cut off, and the induced electromotive force generated by the motor's self-rotation can reverse charge the electrolytic capacitor E1 through the six body diodes of switching tubes T1 to T6. Only when the switching tube K1 is turned on at this time will the braking effect be achieved.

[0077] To solve the problem that when the induced electromotive force generated by the motor's self-rotation is lower than the bus voltage, it can still charge the bus, see Figure 5 , the present application provides a pressure relief circuit 50.

[0078] The pressure relief circuit 50 includes a series-connected voltage regulator tube TV1 and a resistor R1, and is connected in parallel between the positive and negative poles of the bus DC power supply.

[0079] See Figure 5 , the pressure relief circuit 50 is located between the electrolytic capacitor E1 and the IPM module 20.

[0080] Select the model of the voltage regulator TV1 according to the magnitude of the stable bus voltage. It is required that the operating voltage of the voltage regulator TV1 is greater than the stable bus voltage. In this way, when the bus voltage rises, the voltage regulator TV1 will be broken down to connect the pressure relief circuit 50, and the raised voltage will be consumed through the resistor R1.

[0081] In some embodiments of the present application, refer to Figure 4 and Figure 5 , the motor control system further includes a voltage acquisition module 60, which is used to acquire the bus voltage Vdc.

[0082] The voltage acquisition module 60 may include a plurality of voltage dividing resistors connected in series between the positive and negative poles of the bus DC power supply.

[0083] For example, a first voltage dividing resistor and a second voltage dividing resistor are connected in series between the positive and negative poles of the bus DC power supply.

[0084] The main control unit calculates the bus voltage Vdc by obtaining the voltage of the voltage acquisition module 60 for monitoring the bus voltage.

[0085] In some embodiments of the present application, the motor control system further includes a control unit, which is configured to repeatedly control the opening and closing of three switching tubes T2, switching tube T4, and switching tube T6 simultaneously when receiving a motor braking instruction. After the bus voltage rises to reach the operating voltage of the voltage regulator TV1, the raised voltage is consumed through the resistor R1.

[0086] While raising the bus voltage, the bus voltage is monitored in real time. When the bus voltage rises beyond the threshold voltage, the duty cycle of the same PWM signal simultaneously sent to the switching tubes T2, T4, and T6 is reduced, the rising speed of the bus voltage is reduced, and at the same time, the reduction speed of the motor speed is slowed down.

[0087] Wherein the operating voltage of the voltage regulator TV1 is less than the threshold voltage.

[0088] For example, if the stable bus voltage is set to Vdc, the operating voltage of the voltage regulator TV1 can be set to 10%*Vdc, and the threshold voltage can be set to 25%*Vdc.

[0089] Refer to Figure 5 , during motor braking, take the two phases of U phase and V phase as an example for illustration.

[0090] During motor braking, it is necessary to simultaneously control the opening and closing of the switching tube T2 and the switching tube T4, that is, the switching tube T2 and the switching tube T4 are simultaneously connected and the switching tube T2 and the switching tube T4 are simultaneously disconnected.

[0091] First, send the same PWM signal to the switching tube T2 and the switching tube T4 to control both the switching tube T2 and the switching tube T4 to be connected.

[0092] At this time, the current direction is: from the U-phase winding → the switching tube T2 → the switching tube T4 → the V-phase winding. At this time, the U-phase and V-phase windings are equivalent to being short-circuited, and the current is relatively large.

[0093] At this time, turn off the switching tubes T2 and T4. Since the current in the winding inductance cannot change suddenly, the current direction is: U-phase winding → the body diode of the switching tube T1 → the positive pole of the bus DC power supply → the electrolytic capacitor E1 → the negative pole of the bus DC power supply → the body diode of the switching tube T4 → the V-phase winding. The bus voltage rises, and the electrical energy is converted from rotational kinetic energy into electrical energy.

[0094] Repeatedly control the on and off of the switching tubes T2, T4, and T6, and the bus voltage rises rapidly.

[0095] When the bus voltage rises to the operating voltage of the voltage regulator diode TV1, the voltage regulator diode TV1 operates and conducts. At this time, there will be current flowing through the resistor R1, and the electrical energy is consumed, and the bus voltage returns to normal.

[0096] In this way, the kinetic energy of the motor's self-rotation is converted into the heat generated by the resistor R1, and the motor speed drops rapidly.

[0097] The voltage regulator diode TV1 is an active device, which reduces costs, and relies on its operating voltage to open and relieve pressure, saving relevant circuit design and reducing system complexity.

[0098] It should be noted that even when the induced electromotive force generated by the motor braking is less than the bus voltage, but since when the control switching tubes T2 and T4 are both connected, the U-phase and V-phase windings are equivalent to being short-circuited, a large current will still be generated. Therefore, the electrolytic capacitor E1 will still be charged.

[0099] Therefore, by adopting the pressure relief circuit 50 involved in the present application, there is no need to cut off the power supply, and the bus can also be charged when the induced electromotive force generated by the motor braking is less than the bus voltage, realizing rapid elevation of the bus voltage and realizing motor braking.

[0100] In some embodiments of the present application, the frequency of the PWM signal is consistent with the motor driving frequency, for example, 7KHz is adopted.

[0101] In order to monitor the motor speed during the motor braking process and realize closed-loop control of the motor speed, refer to Figure 6 and Figure 7 , in some embodiments of the present application, the motor control system further includes a speed detection unit, which is used to detect the self-rotation speed of the motor when the motor brakes.

[0102] In some embodiments of the present application, the speed detection unit includes voltage-dividing resistors connected in parallel to each of at least two of the switching tubes T2, T4, and T6.

[0103] See Figure 6 , the rotational speed detection unit may include voltage-dividing resistors R2 and R3 connected in parallel across the two ends of the switching transistor T2, and voltage-dividing resistors R4 and R5 connected in parallel across the two ends of the switching transistor T4.

[0104] During motor braking, taking the two phases of U-phase and V-phase as an example for illustration.

[0105] When the motor rotates freely during braking, since the winding cuts the magnetic induction line, according to the electromagnetic induction law, a sinusoidal induced voltage will be generated between the U-phase and V-phase, and the frequency is proportional to the motor speed.

[0106] When controlling the turn-off of the switching transistor T2 and the switching transistor T4, the induced voltage will be divided by the voltage-dividing resistors R2, R3 and the voltage-dividing resistors R4, R5.

[0107] For example, the voltage value between the voltage-dividing resistors R2 and R3 can be collected, and the voltage value between the voltage-dividing resistors R4 and R5 can be collected.

[0108] This voltage value is collected by the main control unit, and the real-time speed of the motor can be obtained based on this voltage value. The acquisition process of this part is realized by using existing technical means and will not be elaborated here.

[0109] Similarly, when the rotational speed detection unit includes a voltage-dividing resistor connected in parallel across the two ends of the switching transistor T4 and a voltage-dividing resistor connected in parallel across the two ends of the switching transistor T6, the real-time speed of the motor can also be obtained.

[0110] See Figure 7 , the rotational speed detection unit may also include voltage-dividing resistors R2 and R3 connected in parallel across the two ends of the switching transistor T2, voltage-dividing resistors R4 and R5 connected in parallel across the two ends of the switching transistor T4, and voltage-dividing resistors R6 and R7 connected in parallel across the two ends of the switching transistor T6.

[0111] Similarly, by collecting the voltage value between the voltage-dividing resistors R2 and R3, the voltage value between the voltage-dividing resistors R4 and R5, and the voltage value between the voltage-dividing resistors R6 and R7, the real-time speed of the motor can also be obtained.

[0112] By setting the rotational speed detection unit, during the motor braking process, the motor speed can be obtained in real time to achieve closed-loop control of the motor speed.

[0113] In order to achieve accurate control of the motor speed, in some embodiments of the present application, see Figure 8 , a flowchart showing the control of the motor speed is shown.

[0114] The following is described by taking two speed reduction methods as examples.

[0115] The first one is that the motor stops quickly during normal operation, that is, the target speed is zero.

[0116] Repeatedly control the on and off of switching transistors T2, T4, and T6, where switching transistors T2, T4, and T6 are turned on and off simultaneously.

[0117] First, send PWM signals with the same large duty cycle (e.g., 80%) to switching transistors T2, T4, and T6 to control the connection of switching transistors T2, T4, and T6. At this time, each winding is equivalent to a short circuit, and the induced electromotive force generated by the self-rotation of the motor will generate a large short-circuit current in the winding.

[0118] At this time, turn off switching transistors T2, T4, and T6. Since the current in the winding inductance cannot change suddenly, the current in the motor winding continues to flow through the body diode in the switching transistor to charge the electrolytic capacitor E1, and the bus voltage rises.

[0119] The larger the duty cycle of the PWM signal, the faster the bus voltage rises.

[0120] Repeatedly control the on and off of switching transistors T2, T4, and T6, and the bus voltage rises rapidly.

[0121] When the bus voltage rises to the operating voltage of the zener diode, the zener diode operates and conducts, and the electrolytic capacitor E1 discharges through the resistor R1. At this time, there will be current flowing through the resistor R1, and the electrical energy is consumed, and the bus voltage drops back to normal.

[0122] Through the above process, the kinetic energy of the motor self-rotation is converted into the heat of the resistor R1, and the motor speed drops rapidly until it stops.

[0123] During this process, the motor speed is monitored in real time. When the speed is equal to zero, the control of the switching transistor is stopped.

[0124] During the above process, it is possible that during the discharge process of the electrolytic capacitor E1, due to the power limitation of the resistor R1, when charging after discharging, the bus voltage will exceed the threshold voltage, causing damage to the electrolytic capacitor E1.

[0125] Therefore, referring to Figure 9 , it is necessary to monitor in real time whether the bus voltage reaches the threshold voltage.

[0126] When the bus voltage reaches the threshold voltage, reduce the duty cycle of the PWM signals sent to switching transistors T1, T3, and T5 to reduce the rising speed of the bus voltage.

[0127] The duty cycle of the PWM signal can fluctuate between 20% and 80%.

[0128] Still referring to Figure 8 , the second case is that when the motor is running normally, the speed drops rapidly to a certain value, that is, the target speed is non-zero.

[0129] Repeatedly control the on and off of switching transistors T2, T4, and T6 until the motor speed drops to the target speed.

[0130] First, send PWM signals with the same large duty cycle (e.g., 80%) to switching transistors T2, T4, and T6 to control them to be all connected. At this time, each winding is equivalent to a short circuit, and the induced electromotive force generated by the motor's self-rotation will generate a large short-circuit current in the winding.

[0131] At this time, turn off switching transistors T2, T4, and T6. Since the current in the winding inductance cannot change suddenly, the current in the motor winding continues to flow through the body diode in the switching transistor and charges the electrolytic capacitor E1, causing the bus voltage to rise.

[0132] The larger the duty cycle of the PWM signal, the faster the bus voltage rises.

[0133] Repeatedly control the on and off of switching transistors T2, T4, and T6, and the bus voltage rises rapidly.

[0134] When the bus voltage rises to the operating voltage of the zener diode TV1, the zener diode TV1 operates and conducts, and the electrolytic capacitor E1 discharges through the resistor R1. At this time, there will be current flowing through the resistor R1, and the electrical energy is consumed, and the bus voltage drops back to normal.

[0135] Through the above process, the kinetic energy of the motor's self-rotation is converted into heat generated by the resistor R1, and the motor speed drops rapidly.

[0136] During the process of the motor speed dropping, in order to control the motor speed to drop to the target speed, during the entire motor braking process, the control unit monitors the motor speed in real time.

[0137] When the motor speed is close to the target speed, for example, when the difference between the motor speed detected in real time and the target speed is less than the preset range, reduce the duty cycle of the PWM signal, reduce the rising speed of the bus voltage, and also reduce the decreasing speed of the motor speed.

[0138] When the motor speed reaches the target speed, the motor enters the normal drive control of the motor, that is, FOC control, and stops controlling the switching transistor.

[0139] Similarly, refer to Figure 9 , in the above process, it is possible that during the discharge process of the electrolytic capacitor E1, due to the power limitation of the resistor R1, when charging again after discharge, the bus voltage will exceed the threshold voltage, causing damage to the electrolytic capacitor E1.

[0140] Therefore, it is necessary to monitor in real time whether the bus voltage reaches the threshold voltage.

[0141] When the bus voltage reaches the threshold voltage, reduce the duty cycle of the PWM signals sent to switching transistors T2, T3, and T4 to reduce the rising speed of the bus voltage.

[0142] The duty cycle of the PWM signal can fluctuate between 20% and 80%. When reducing the duty cycle of the PWM signal, the duty cycle can be gradually reduced from 80%.

[0143] When determining whether the bus voltage reaches the threshold voltage, the response should be fast; otherwise, an excessive voltage will be formed across the electrolytic capacitor, resulting in breakdown.

[0144] Therefore, to avoid this situation, refer to Figure 10 and it is possible to judge the rising trend of the bus voltage by monitoring the voltage rising rate of the bus voltage, output an alarm reminder, and control the bus voltage to drop in advance to prevent damage to the electrolytic capacitor due to the bus voltage exceeding the threshold voltage.

[0145] This application also relates to an air conditioner, which includes a refrigerant circulation circuit that circulates the refrigerant in a circuit composed of a compressor, a condenser, an expansion valve, and an evaporator.

[0146] The air conditioner further includes a compressor for compressing the low-temperature and low-pressure refrigerant gas into a high-temperature and high-pressure refrigerant gas and discharging it to the condenser.

[0147] An outdoor heat exchanger and an indoor heat exchanger, where one operates as a condenser and the other operates as an evaporator.

[0148] When the air conditioner is cooling, the indoor heat exchanger operates as an evaporator, cooperating with the indoor fan to discharge cold air into the room, and the outdoor heat exchanger operates as a condenser, cooperating with the outdoor fan to discharge the generated hot air to the outside.

[0149] When the air conditioner is heating, the indoor heat exchanger operates as a condenser, cooperating with the indoor fan to discharge hot air into the room, and the outdoor heat exchanger operates as an evaporator, cooperating with the outdoor fan to discharge the generated cold air to the outside.

[0150] The air conditioner further includes a variable-frequency topology circuit structure.

[0151] The variable-frequency topology structure refers to the above-mentioned and Figures 2 to 7 , and includes a rectifying unit 30, a PFC circuit 40, and an IPM module 20.

[0152] The rectifying unit 30 is used to rectify three-phase alternating current into direct current. The PFC circuit 40 is connected between the output terminal of the rectifying unit 30 and the electrolytic capacitor E1 for power factor correction of the power supply. The electrolytic capacitor E1 outputs a stable bus DC power supply. The IPM module 20 is used to invert the bus DC power supply into three-phase voltage to supply power to the motor.

[0153] The motor control system used for the motor adopts the motor control system as described above, and the motor can be a motor for a compressor, a motor for an outdoor fan, or a motor for an indoor fan.

[0154] The air conditioner includes a pressure relief circuit.

[0155] The pressure relief circuit is the pressure relief circuit 50 as above, including a series-connected voltage stabilizing diode TV1 and a resistor R1, and is connected in parallel between the positive and negative poles of the bus DC power supply.

[0156] The pressure relief circuit 50 is located between the electrolytic capacitor E1 and the IPM module 20.

[0157] Select the model of the voltage stabilizing diode TV1 according to the magnitude of the stable bus voltage. It is required that the operating voltage of the voltage stabilizing diode TV1 is greater than the stable bus voltage. In this way, when the bus voltage rises, the voltage stabilizing diode TV1 will be broken down to connect the pressure relief circuit 50, and the elevated voltage will be consumed through the resistor R1.

[0158] In some embodiments of the present application, the air conditioner further includes a control unit, which is configured to repeatedly control the opening and closing of the three switching tubes T2, the switching tube T4, and the switching tube T6 simultaneously when receiving a motor braking instruction. After the bus voltage rises to reach the operating voltage of the voltage stabilizing diode TV1, the elevated voltage is consumed through the resistor R1.

[0159] While raising the bus voltage, monitor the bus voltage in real time. When the bus voltage rises beyond the threshold voltage, reduce the duty cycle of the same PWM signal sent to the switching tubes T2, T4, and T6 simultaneously, reduce the rising speed of the bus voltage, and at the same time slow down the reduction speed of the motor speed.

[0160] Controlling the motor with the motor control system as described above can monitor the speed in real time during motor braking, and without cutting off the power supply, it can avoid the induced electromotive force generated by motor braking from raising the bus voltage, and at the same time reduce the motor speed, realizing reliable braking of the motor and improving the working reliability of the air conditioner.

[0161] In the description of the above embodiments, the specific features, structures, materials, or characteristics can be combined in a suitable manner in any one or more embodiments or examples.

[0162] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A motor control system, characterized in that, Comprising: A rectifying unit for rectifying three-phase alternating current into direct current; A PFC circuit connected between the output terminal of the rectifying unit and the electrolytic capacitor for power factor correction of the power supply, and the electrolytic capacitor outputs a stable bus DC power supply; An IPM module for inverting the bus DC power supply into three-phase voltage to supply power to the motor; A pressure relief circuit connected in parallel to the bus and located at the front end of the IPM module, and the pressure relief circuit includes a series-connected voltage stabilizing diode and a resistor; A voltage acquisition module for acquiring the bus voltage; A control unit configured to, when receiving a motor braking instruction, perform the following: Repeatedly and simultaneously control the opening and closing of three switching tubes in three lower bridge arms of the IPM module. After the bus voltage rises to reach the operating voltage of the voltage stabilizing diode, the elevated voltage is consumed through the resistor; While raising the bus voltage, monitor the bus voltage in real time. When the bus voltage rises beyond the threshold voltage, reduce the duty cycle of the same PWM signal simultaneously sent to the three switching tubes; Wherein, the same PWM signal is simultaneously sent to the three switching tubes in the three lower bridge arms to connect the three switching tubes; The stable bus voltage, the operating voltage of the voltage stabilizing diode, and the threshold voltage increase in sequence.

2. The motor control system according to claim 1, characterized in that, The motor control system further includes: A speed detection unit for detecting the motor speed during motor braking; The control unit is further configured to: Judge whether the target speed of the motor is zero. If so, proceed to S1; if not, proceed to S2; S1: Repeatedly and simultaneously control the opening and closing of three switching tubes in three lower bridge arms of the IPM module until the motor stops. Among them, the same PWM signal with a first duty cycle is simultaneously sent to the three switching tubes in the three lower bridge arms to connect the three switching tubes; S2: Repeatedly and simultaneously control the opening and closing of three switching tubes in three lower bridge arms of the IPM module. Among them, the same PWM signal with a first duty cycle is simultaneously sent to the three switching tubes in the three lower bridge arms to connect the three switching tubes; During the process of reducing the motor speed, judge in real time whether the motor speed is close to the target speed. If so, reduce the duty cycle of the same PWM signal simultaneously sent to the three switching tubes in the three lower bridge arms until the speed reaches the target speed. If not, return to S2; After the speed reaches the target speed, switch back to normal motor drive control.

3. The motor control system according to claim 2, wherein The speed detection unit includes voltage-dividing resistors connected in parallel to each of at least two of the three switching tubes in the three lower bridge arms.

4. The motor control system according to claim 1, characterized in that, The control unit is further configured to: While raising the bus voltage, also monitor the voltage rising rate of the bus voltage in real time; When the voltage rising rate reaches a preset threshold, output an alarm reminder.

5. The motor control system according to claim 1, wherein The voltage acquisition module includes a plurality of voltage-dividing resistors connected in series between the positive and negative poles of the bus DC power supply.

6. The motor control system according to claim 1, wherein The frequency of the PWM signal is consistent with the motor driving frequency.

7. An air conditioner, characterized in that, It includes: A refrigerant circulation circuit that circulates refrigerant in a circuit composed of a compressor, a condenser, an expansion valve, and an evaporator; A compressor that compresses low-temperature and low-pressure refrigerant gas into high-temperature and high-pressure refrigerant gas and discharges it to the condenser; An outdoor heat exchanger and an indoor heat exchanger, where one operates as a condenser and the other operates as an evaporator; A variable-frequency topology circuit structure including a rectification unit, a PFC circuit, and an IPM module. The rectification unit rectifies three-phase alternating current into direct current. The PFC circuit is connected between the output terminal of the rectification unit and an electrolytic capacitor to perform power factor correction on the power supply. The electrolytic capacitor outputs a stable bus DC power supply. The IPM module converts the bus DC power supply into three-phase voltage to supply power to a motor, and the motor is a compressor motor, an outdoor fan motor for outdoor heat exchanger heat exchange, or an indoor fan motor for indoor heat exchanger heat exchange; A pressure relief circuit that is connected in parallel to the bus and is located at the front end of the IPM module. The pressure relief circuit includes a zener diode and a resistor connected in series; A voltage acquisition module that is used to acquire the bus voltage; A control unit that is configured to perform the following when receiving a motor braking instruction: Repeatedly and simultaneously control the opening and closing of three switching tubes in three lower bridge arms of the IPM module. After the bus voltage rises to reach the operating voltage of the zener diode, the elevated voltage is consumed through the resistor; While raising the bus voltage, monitor the bus voltage in real time. When the bus voltage rises beyond the threshold voltage, reduce the duty cycle of the same PWM signal simultaneously sent to the three switching tubes; Among them, the same PWM signal is simultaneously sent to three switching tubes in three lower bridge arms to connect the three switching tubes; The stable bus voltage, the operating voltage of the zener diode, and the threshold voltage increase in sequence.

8. The air conditioner according to claim 7, wherein The air conditioner further includes: A rotational speed detection unit that is used to detect the motor rotational speed during motor braking; The control unit is further configured to: Judge whether the target rotational speed of the motor is zero. If so, proceed to S1. If not, proceed to S2; S1: Repeatedly and simultaneously control the opening and closing of three switching tubes in three lower bridge arms of the IPM module until the motor stops. Among them, the same PWM signal with a first duty cycle is simultaneously sent to the three switching tubes in three lower bridge arms to connect the three switching tubes; S2: Repeatedly and simultaneously control the opening and closing of three switching tubes in three lower bridge arms of the IPM module. Among them, the same PWM signal with a first duty cycle is simultaneously sent to the three switching tubes in three lower bridge arms to connect the three switching tubes; During the process of reducing the motor rotational speed, judge in real time whether the motor rotational speed is close to the target rotational speed. If so, reduce the duty cycle of the same PWM signal simultaneously sent to the three switching tubes in three lower bridge arms until the rotational speed reaches the target rotational speed. If not, return to S2; After the rotational speed reaches the target rotational speed, switch back to normal motor drive control.

9. The air conditioner according to claim 8, wherein the rotation speed detection unit includes voltage dividing resistors connected in parallel to each of at least two of the three switching transistors in the three lower bridge arms.

10. The air conditioner according to claim 7, characterized in that, The control unit is further configured to: while boosting the bus voltage, also monitor the voltage rise rate of the bus voltage in real time; when the voltage rise rate reaches a preset threshold, output an alarm reminder.

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