Method for suppressing resonance conduction disturbance of variable frequency air conditioner cross flow fan and air conditioner

Abstract

The present application relates to the technical field of electromagnetic compatibility of variable frequency air conditioner, and particularly relates to a method for suppressing critical resonance conduction disturbance of cross-flow fan of variable frequency air conditioner and an air conditioner. The method comprises the following steps: source end harmonic reduction step: the PWM switching speed threshold is lowered to below the lowest wind speed operation speed, so that the full wind speed is forced to operate in five-stage PWM; resonance frequency band offset step: the PWM carrier frequency is adjusted to a target frequency offset from the system torsional natural resonance frequency to reduce the modulation depth of resonance on the parasitic capacitance; path isolation blocking step: the electric heating wire part extending outside the electric control box is folded back into the box and away from the motor shell, and the motor cable is independently wired to block the two conduction paths of common mode current. The present application effectively solves the problems of complex disturbance caused by deep mutual coupling of mechanical resonance, control strategy and parasitic parameters, and the problems of batch consistency and insufficient robustness in all working conditions. Moreover, no hardware change is needed, and the cost is low and easy to mass-produce.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic compatibility technology for variable frequency air conditioners, specifically to a method for suppressing resonant conducted interference from the cross-flow fan of a variable frequency air conditioner and an air conditioner thereof. Background Technology

[0002] As the air conditioning industry continues to evolve towards higher energy efficiency, increasing the diameter of the indoor unit's cross-flow fan has become a common technical approach to improve heat exchange efficiency. However, in actual research and development, it has been discovered that this seemingly straightforward modification can trigger extremely unusual electromagnetic compatibility issues.

[0003] Specifically, when the diameter of the cross-flow fan in the inverter air conditioner wall-mounted unit was gradually increased from 90.4mm to 106mm while using a mature electronic control scheme, the conducted interference voltage remained normal, with a margin consistently above 5dB. However, when the diameter was further increased to 108mm, under completely unchanged conditions such as motor control strategy and overall wiring, the conducted interference voltage at the low fan speed suddenly and drastically deteriorated, with a margin of only 0.1dB, which seriously exceeded the standard limit. In stark contrast, the interference level at the medium and high fan speeds remained normal.

[0004] This phenomenon exhibits typical characteristics of a critical abrupt change, and at least three aspects contradict conventional understanding: First, the fan itself is made of plastic, and traditional theory holds that it should not affect EMC performance; second, the interference level does not deteriorate slowly with increasing diameter, but rather suddenly spikes after crossing a certain size threshold; third, the interference at low speeds is far more severe than at high speeds, which is exactly the opposite of the general rule that increased load leads to increased interference.

[0005] Through systematic engineering investigation and mechanism analysis, the underlying causes of the aforementioned anomalies were clarified. When the fan diameter increases to a critical size, the moment of inertia jumps significantly, causing the first-order torsional natural frequency of the fan-motor system to drop to the low-speed rotational frequency (approximately 13.67Hz), inducing continuous low-frequency mechanical resonance. The periodic, minute mechanical displacements generated by this resonance dynamically modulate the parasitic capacitance between the motor windings, wiring, and the chassis, causing the parasitic capacitance value to fluctuate periodically with mechanical vibration. This, in turn, modulates the amplitude of the motor's high-frequency PWM switching harmonics, generating numerous high-frequency sideband disturbances distributed on both sides of the carrier wave. Simultaneously, under low-speed, low-speed conditions, the motor's current loop bandwidth is limited, and its resistance to load disturbances is weak. The micro-disturbances caused by resonance exacerbate the distortion of the motor's phase current, further increasing the high-frequency harmonic energy, forming an electromechanical positive feedback amplification effect of "low-frequency mechanical resonance modulating high-frequency electrical harmonics." The high-frequency interference, amplified by electromechanical coupling, is conducted outwards through two parasitic coupling channels: one is the parasitic capacitance C1 formed by the electric heating wire and the motor housing, and the other is the parasitic capacitance C2 formed by the contact between the motor cable and other connections in the unit. In heating mode, the electric heating relay is engaged, connecting the electric heating branch to the power supply circuit, and the C1 parasitic channel is activated, allowing high-frequency interference from the motor side to be directly coupled and conducted to the power supply. In cooling mode, the electric heating relay is disengaged, isolating the electric heating branch from the power supply, and the C1 conduction channel fails. Therefore, the interference exceeding the standard in heating mode is much higher than in cooling mode, exhibiting significant differences in operating conditions. A schematic diagram of the interference path verification experiment is shown below. Figure 1 As shown, this ultimately led to severely excessive conducted interference at the low windshield.

[0006] For conducted interference issues induced by structural resonance, conventional industry solutions mainly include optimizing internal wiring, switching PWM modulation modes in high-speed ranges, and fine-tuning the PWM carrier frequency to avoid interference peaks. However, these measures share common shortcomings: none of them consider the dynamic modulation effect of resonance on parasitic capacitance; the control strategy switching only covers high-speed operation and fails to address the root cause of low-speed operation; and the carrier frequency adjustment is not specifically designed around the structural resonance frequency band. Therefore, they cannot effectively solve the complex interference problems caused by the deep coupling between mechanical resonance, control strategy, and parasitic parameters, and have significant shortcomings in terms of mass production consistency and robustness under all operating conditions. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for suppressing conducted interference from the resonant cross-flow fan of a variable frequency air conditioner. This method addresses the problems of existing variable frequency air conditioners where structural resonance is caused by the increase in the diameter of the cross-flow fan to a critical size, resulting in severely excessive conducted interference voltage at low fan speeds. It also addresses the issues that conventional rectification methods cannot effectively solve the complex interference problems caused by the deep coupling between mechanical resonance, control strategies, and parasitic parameters due to the failure to consider the dynamic modulation effect of resonance on parasitic capacitance, and the lack of batch consistency and robustness under all operating conditions.

[0008] To achieve the above objectives, a method for suppressing resonant conducted interference from a cross-flow fan in a variable frequency air conditioner is provided. This method is applied to a variable frequency air conditioner comprising a cross-flow fan, a fan motor, an electrical control box, and an electric heater, and includes the following steps:

[0009] Source harmonic reduction steps: when the fan motor speed is higher than the first threshold, run five-segment PWM; when the speed is lower than the second threshold, run seven-segment PWM. The first threshold is greater than the second threshold. Lower both the first threshold and the second threshold to below the lowest fan speed, so that the fan motor is forced to run five-segment PWM modulation in all actual fan speeds.

[0010] Resonance band offsetting step: Adjust the PWM carrier frequency of the fan motor from the preset frequency to the target frequency. The target frequency is offset from the system's torsional inherent resonance frequency. The system's torsional inherent resonance frequency is the torsional inherent resonance frequency formed by the system composed of the fan motor and the cross-flow fan when the diameter of the cross-flow fan increases to the critical size. The torsional inherent resonance frequency falls back to the rotation frequency range of the air conditioner's low-speed fan.

[0011] Path isolation and blocking steps: Perform wiring adjustments inside the indoor unit, including at least one of the following operations:

[0012] a) Fold back the portion of the electric heating wire extending outside the electrical control box and fix it inside the electrical control box, so that the electric heating wire and the fan motor housing maintain a predetermined distance;

[0013] b) The motor cable of the fan motor is routed along an independent path, so that the motor cable is not in contact with other wiring in the unit.

[0014] Principles and advantages:

[0015] 1. This solution lowers both the first threshold for switching from five-segment PWM to seven-segment PWM and the second threshold for switching from seven-segment PWM to five-segment PWM to below the lowest fan speed, thus forcing the fan motor to run five-segment PWM at all actual fan speeds. This reduces the base number of harmonic energy available for resonant modulation from the source and solves the problem that the low fan speed always runs in seven-segment PWM under the existing hysteresis switching strategy, which becomes the main source of interference.

[0016] 2. This solution reduces the modulation depth of the parasitic capacitance by adjusting the PWM carrier frequency to a target frequency that is offset from the system's torsional resonant frequency, thus solving the problem that conventional carrier frequency adjustments cannot effectively weaken the mechanical-electromagnetic coupling effect because they are not designed for the structural resonant frequency band.

[0017] 3. This solution physically cuts off the two conduction paths of common-mode current generated by resonant modulation by folding the portion of the electric heating wire extending outside the control box back into the box and fixing it away from the motor housing, and by routing the fan motor cable independently without contacting the unit wiring. This solves the problem of poor batch consistency caused by differences in production line wiring. It can also specifically suppress additional coupling interference caused by the electric heating wire connecting to the power supply circuit in heating mode, achieving simultaneous optimization of EMC performance under both cooling and heating conditions.

[0018] 4. This solution can be implemented individually or in combination with source harmonic reduction, resonant frequency band offset, and path isolation and blocking optimization measures, adapting to the interference exceedance levels and structural differences of different models. When the three are implemented simultaneously and in synergy, it can comprehensively solve the systemic interference problem caused by the deep mutual coupling of mechanical resonance, control strategy and parasitic parameters, so that the conducted interference voltage margin of each windshield is increased to more than 4.2dB, the batch consistency and robustness under all operating conditions are significantly improved, and no hardware changes are required, the cost is low and it is easy to mass produce.

[0019] Furthermore, in the source harmonic reduction step, the first threshold is at least 40 r / min lower than the lowest windshield operating speed.

[0020] A minimum 40 r / min difference limit ensures that the hysteresis switching range (the speed band between the first and second thresholds) does not touch the lowest fan speed operating point, avoiding frequent switching of the PWM mode near the lowest fan speed due to speed fluctuations, thus guaranteeing motor control stability. This difference limit provides a minimum deviation reference for setting the first threshold, making the effect of forced operation of the five-segment PWM at all fan speeds independent of minor differences in speed between specific models, and possessing cross-model adaptability.

[0021] Furthermore, in the source harmonic reduction step, the first threshold is selected within the range of 700 r / min to 780 r / min.

[0022] The range of the first threshold value takes into account both upper and lower limits, avoiding both excessively high thresholds that fail to fully cover the windshield range and excessively low thresholds that cause hysteresis control imbalance. This provides a standardized parameter design range for variable frequency air conditioners with different speed specifications, making it highly adaptable.

[0023] Furthermore, in the source harmonic reduction step, the minimum windshield operating speed is 820 r / min, the first threshold is 750 r / min, and the second threshold is 720 r / min.

[0024] This threshold setting enables full coverage of the five-segment PWM across all windshields, while maintaining stable hysteresis switching logic, ensuring motor operational stability while guaranteeing harmonic reduction.

[0025] Furthermore, in the resonant frequency band offset step, the target frequency is in the range of 15kHz to 18kHz and is offset from the system's torsional inherent resonant frequency by at least 2kHz.

[0026] This solution ensures that the PWM main harmonic group and its sideband harmonics avoid the torsional inherent resonance band of the system after the fan diameter increases critically. Simultaneously, the 15-18kHz carrier frequency range balances switching losses and heat dissipation requirements, preventing issues such as increased motor current ripple due to excessively low carrier frequency or increased switching losses due to excessively high carrier frequency. By setting a frequency difference of no less than 2kHz, the coupling range of sideband harmonics generated by resonance can be effectively avoided, blocking the dynamic modulation effect of mechanical resonance on parasitic capacitance. This also balances motor control accuracy and switching losses, preventing performance degradation such as reduced overall noise, temperature rise, and airflow caused by carrier frequency deviation.

[0027] Furthermore, in the resonant frequency band misalignment step, when the fan diameter reaches 108mm, the preset frequency is 20kHz and the target frequency is 16kHz.

[0028] 20kHz is the conventional carrier frequency setting value in the existing technology, and its main harmonic group just falls into the critical resonance modulation sensitive frequency band. After the target frequency is lowered to 16kHz, the main harmonic group is offset from the structural resonance frequency band. At the same time, the 16kHz carrier frequency value reduces the resonance modulation sensitivity while maintaining sufficient control bandwidth to ensure that the dynamic response performance of motor control does not degrade. Moreover, this frequency point is a standard industrial commonly used value and does not increase the design cost of additional EMC filters.

[0029] Furthermore, in operation a) of the path isolation and blocking step, the predetermined spacing is not less than 5mm.

[0030] The parasitic capacitance between the electric heating wire and the fan motor housing is inversely proportional to the distance between them. When the distance is not less than 5mm, the parasitic capacitance C1 is eliminated, and the corresponding conduction path of the common mode current is effectively cut off. At the same time, the 5mm distance requirement is easy to visually inspect and control in actual production line operation, without affecting production efficiency, and takes into account both EMC suppression effect and mass production operability.

[0031] Furthermore, the path isolation and blocking step also includes: adding a fixed point on the wiring path of the motor cable of the fan motor to constrain the motor cable to maintain a non-contact state with other wiring in the unit.

[0032] This solution constrains the motor cable to maintain an independent routing state by adding fixed points along its wiring path. The addition of these fixed points ensures that the relative position of the motor cable to other connections within the unit remains unchanged throughout its entire lifecycle of production, transportation, and use. This eliminates the risk of cable displacement caused by differences in production line operations and long-term vibrations, fundamentally ensuring that the "non-contact state" is effectively maintained in terms of mass production consistency and long-term reliability. It also solves the problem that conventional "optimized routing" solutions rely solely on operator experience and cannot guarantee batch consistency.

[0033] The second objective of this invention is to provide an inverter air conditioner, including an indoor unit, wherein the indoor unit has a cross-flow fan, a fan motor, an electrical control box, an electric heater, and a motor controller;

[0034] The portion of the electric heating wire extending outside the electrical control box is folded back and fixed inside the electrical control box, and there is a predetermined distance between the electric heating wire and the fan motor housing;

[0035] The motor cable of the fan motor is routed along an independent path, keeping it in a non-contact state with other connections in the unit, and fixed points are set along the wiring path of the motor cable to maintain the non-contact state.

[0036] The motor controller is configured to perform a method for suppressing resonant conducted interference from the cross-flow fan of a variable frequency air conditioner.

[0037] The air conditioner in this solution has a standardized wiring structure inside the indoor unit when it leaves the factory—the electric heating wire is folded back into the box and kept away from the motor housing, and the motor cable is run independently and has a fixing point—so that the EMC performance of the product in mass production on the production line no longer depends on the manual experience of the operators; at the same time, the motor controller is configured to execute the control process of the above method, so that the air conditioner can automatically maintain a conducted interference margin of more than 4.2dB under all operating conditions (cooling / heating, all fan speeds), realizing the integrated design of EMC performance, product structure and control logic.

[0038] Furthermore, the predetermined distance between the electric heating wire and the fan motor housing is not less than 5mm.

[0039] The spacing requirements of this solution provide clear quantitative indicators for the product structure design. The quality inspection process can determine the pass rate through simple measurement, ensuring that each product leaving the factory has a consistent path isolation effect. At the same time, the minimum spacing requirement of 5mm does not affect the compact space layout design inside the indoor unit. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the interference path verification experiment;

[0041] Figure 2 The conducted disturbance voltage spectrum of the faulty prototype under low wind speed.

[0042] Figure 3 This is a flowchart illustrating a method for suppressing resonant conducted interference from a cross-flow fan in a variable frequency air conditioner, according to an embodiment of the present invention.

[0043] Figure 4 This is a diagram showing the relationship between the seven-segment PWM control logic and conducted disturbance voltage of the faulty prototype of this invention under high wind speed.

[0044] Figure 5 This is a diagram showing the relationship between the five-segment PWM control logic and the conducted disturbance voltage of the faulty prototype of this invention under high wind speed. Detailed Implementation

[0045] The following detailed description illustrates the specific implementation method:

[0046] Example

[0047] This embodiment uses a certain model of inverter air conditioner as the implementation object. The indoor unit of this air conditioner includes a cross-flow fan, a fan motor that drives the cross-flow fan, an electrical control box, an electric heater, and a motor controller. During the development of this model, the diameter of the cross-flow fan was increased from 90.4mm to 106mm and then to 108mm, resulting in three comparison models: AM (90.4mm), BM (106mm), and CM (108mm).

[0048] With the motor control strategy and overall wiring remaining completely unchanged, low-profile conducted interference voltage tests were conducted on the three models according to GB / T 17626.6 "Electromagnetic Compatibility Testing and Measurement Techniques - Conducted Interference Immunity from Radio Frequency Field Induction". The test results showed that the AM (90.4mm) and BM (106mm) models had a stable low-profile conducted interference voltage margin of over 5dB, indicating normal performance; however, the CM (108mm) model's low-profile conducted interference voltage margin dropped sharply to only 0.1dB, significantly exceeding the enterprise standard (≥3dB) limit. Its conducted interference voltage spectrum is as follows: Figure 2 As shown in the conducted interference test of CISPR14 (and the corresponding national standard GB 4343.1): CISPR14 VOLTAGE MAINS QP: refers to the quasi-peak value of the power supply terminal interference voltage. CISPR14 VOLTAGE MAINS AV: refers to the average value of the power supply terminal interference voltage. Under medium to high wind conditions, the interference level of the CM type remains normal, exhibiting a clear critical abrupt change characteristic.

[0049] For the aforementioned CM-type faulty prototype, rectification was implemented according to the relevant steps of a method for suppressing resonant conducted interference in a variable frequency air conditioner cross-flow fan, and the results were basically as follows: Figure 3 As shown, it includes the following steps:

[0050] Step 1: Source Harmonic Reduction Steps

[0051] In the existing technology, this model uses a hysteresis switching strategy to control the PWM modulation mode: when the fan motor speed is higher than the first threshold (980 r / min in this embodiment), it operates a five-segment PWM; when the fan motor speed is lower than the second threshold (950 r / min in this embodiment), it operates a seven-segment PWM, where the first threshold is greater than the second threshold. The CM model's low fan speed is 820 r / min, consistently lower than the second threshold of 950 r / min, thus always operating in the seven-segment PWM with a high number of switching operations, resulting in rich harmonic components and becoming a major source of interference that can be modulated resonantly. The relationship between the seven-segment PWM control logic and the interference voltage of the faulty prototype at the high fan speed (970 r / min) is as follows: Figure 4 As shown.

[0052] In this embodiment, both the first and second thresholds are lowered to below the lowest fan speed. Specifically, the first threshold is lowered from 980 r / min to 750 r / min, and the second threshold is lowered from 950 r / min to 720 r / min. The actual operating speed range of the CM type at each fan speed is 820 r / min to 1020 r / min. Both the lowered first threshold of 750 r / min and the second threshold of 720 r / min are lower than the lowest fan speed of 820 r / min. Therefore, the fan motor is forced to operate a five-segment PWM with fewer switching cycles at all actual fan speeds, reducing the base harmonic energy available for resonant modulation from the source. The correspondence between the five-segment PWM control logic and the conducted interference voltage of the rectified prototype at the high fan speed (970 r / min) is as follows: Figure 5 As shown.

[0053] Furthermore, in this embodiment, the lowered first threshold of 750 r / min is lower than the lowest fan speed of 820 r / min, with a difference of 70 r / min. When adapting to different models, the difference between the first threshold and the lowest fan speed can be adjusted according to the speed range and motor characteristics of the specific model. Preferably, this difference is not less than 40 r / min to ensure that the hysteresis switching range does not touch the lowest fan speed operating point, avoiding frequent switching of the PWM mode near the lowest fan speed due to speed fluctuations. At the same time, the first threshold is preferably set at 750 r / min. When adapting to models with different speed specifications, it can be selected within the range of 700 r / min to 780 r / min, which ensures the full fan speed five-segment PWM coverage effect while reserving a margin for adaptation adjustment to different models.

[0054] Step Two: Resonance Band Misalignment Step

[0055] The PWM carrier frequency of the fan motor is adjusted from the preset frequency to the target frequency. The target frequency is offset from the system's torsional natural resonance frequency. The system's torsional natural resonance frequency is the torsional natural resonance frequency formed by the system consisting of the fan motor and the cross-flow fan when the diameter of the cross-flow fan increases to a critical size. The torsional natural resonance frequency falls back to the rotation frequency range of the air conditioner's low-speed fan.

[0056] The system torsional resonant frequency of a 108mm critical diameter fan falls into the low-speed operating frequency band (i.e., the rotation frequency range of an air conditioner fan at low speed), which easily creates a low-frequency modulation effect on the conventional 20kHz PWM high-frequency carrier, generating a large number of excessive sideband harmonics.

[0057] In this embodiment, the PWM carrier frequency is adjusted from a preset frequency of 20kHz to a target frequency of 16kHz, thus shifting the main harmonic group and the structural resonant frequency band by 4kHz, significantly reducing the modulation depth of the structural resonance on the parasitic capacitance. When adapting to different models, the target frequency can be selected in the range of 15kHz to 18kHz to achieve a shift of at least 2kHz from the system's torsional natural resonant frequency.

[0058] Step 3: Path Isolation and Blocking Steps

[0059] This embodiment performs wiring adjustments inside the indoor unit, specifically including the following operations:

[0060] Fold back the portion of the electric heating wire that extends outside the control box and fix it inside the control box, so that the electric heating wire is laid away from the fan motor housing with a spacing of not less than 5mm, thereby eliminating the parasitic capacitance C1 between the electric heating wire and the motor housing.

[0061] The fan motor cable is routed along an independent path to prevent it from contacting other wiring within the unit, thereby eliminating the parasitic capacitance C2 between the motor cable and the unit wiring.

[0062] In addition, fixing points (such as wire clips, cable ties, etc.) are added to the wiring path of the motor cables to constrain the motor cables to maintain an independent wiring state and ensure wiring consistency in mass production on the production line.

[0063] Verification results

[0064] Five CM-type prototypes, after being rectified according to the above steps, underwent conducted disturbance voltage testing according to GB / T 17626.6. The test covered all operating conditions (cooling / heating mode, low / medium / high fan speed). After rectification, the conducted disturbance voltage margin at each fan speed of the prototypes was improved to over 4.2dB, meeting and exceeding the enterprise standard limit requirement (≥3dB). The rectified prototypes maintained consistently good EMC performance in both cooling and heating modes, eliminating EMC performance fluctuations caused by mode switching, and significantly improving batch consistency and robustness across all operating conditions. Simultaneously, the forced operation of the five-segment PWM across all fan speeds reduced the switching losses of the IPM module, incidentally improving the reliability of the electrical control components. Noise, airflow, and other performance indicators all met design requirements. The entire rectification process did not involve any hardware changes; it was achieved only through software parameter adjustments and standardized wiring procedures, and can be directly implemented on existing production lines.

[0065] This embodiment also provides an inverter air conditioner, including an indoor unit, which has a cross-flow fan, a fan motor, an electrical control box, an electric heater, and a motor controller;

[0066] The portion of the electric heating wire extending outside the electrical control box is folded back and fixed inside the electrical control box, and there is a predetermined distance between the electric heating wire and the fan motor housing;

[0067] The motor cable of the fan motor is routed along an independent path, keeping it in a non-contact state with other connections in the unit, and fixed points are set along the wiring path of the motor cable to maintain the non-contact state.

[0068] The motor controller is configured to perform the above-described method for suppressing resonant conducted interference from the cross-flow fan of a variable frequency air conditioner.

[0069] The air conditioner in this solution has a standardized wiring structure inside the indoor unit when it leaves the factory—the electric heating wire is folded back into the box and kept away from the motor housing, and the motor cable is run independently and has a fixing point—so that the EMC performance of the product in mass production on the production line no longer depends on the manual experience of the operators; at the same time, the motor controller is configured to execute the control process of the above method, so that the air conditioner can automatically maintain a conducted interference margin of more than 4.2dB under all operating conditions (cooling / heating, all fan speeds), realizing the integrated design of EMC performance, product structure and control logic.

[0070] The predetermined distance between the electric heating wire and the fan motor housing is not less than 5mm.

[0071] The spacing requirements of this solution provide clear quantitative indicators for the product structure design. The quality inspection process can determine the pass rate through simple measurement, ensuring that each product leaving the factory has a consistent path isolation effect. At the same time, the minimum spacing requirement of 5mm does not affect the compact space layout design inside the indoor unit.

[0072] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, based on the guidance provided in this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for suppressing resonant conducted interference from a cross-flow fan in a variable frequency air conditioner, applied to a variable frequency air conditioner comprising a cross-flow fan, a fan motor, an electrical control box, and an electric heater, characterized in that, Includes the following steps: Source harmonic reduction steps: when the fan motor speed is higher than the first threshold, run five-segment PWM; when the speed is lower than the second threshold, run seven-segment PWM. The first threshold is greater than the second threshold. Lower both the first threshold and the second threshold to below the lowest fan speed, so that the fan motor is forced to run five-segment PWM modulation in all actual fan speeds. Resonance band offsetting step: Adjust the PWM carrier frequency of the fan motor from the preset frequency to the target frequency. The target frequency is offset from the system's torsional inherent resonance frequency. The system's torsional inherent resonance frequency is the torsional inherent resonance frequency formed by the system composed of the fan motor and the cross-flow fan when the diameter of the cross-flow fan increases to the critical size. The torsional inherent resonance frequency falls back to the rotation frequency range of the air conditioner's low-speed fan. Path isolation and blocking steps: Perform wiring adjustments inside the indoor unit, including at least one of the following operations: a) Fold back the portion of the electric heating wire extending outside the electrical control box and fix it inside the electrical control box, so that the electric heating wire and the fan motor housing maintain a predetermined distance; b) The motor cable of the fan motor is routed along an independent path, so that the motor cable is not in contact with other wiring in the unit.

2. The method for suppressing resonant conducted interference from a variable frequency air conditioner cross-flow fan according to claim 1, characterized in that, In the source harmonic reduction step, the first threshold is at least 40 r / min lower than the lowest windshield operating speed.

3. The method for suppressing resonant conducted interference from a variable frequency air conditioner cross-flow fan according to claim 2, characterized in that, In the source harmonic reduction step, the first threshold is selected in the range of 700r / min to 780r / min.

4. The method for suppressing resonant conducted interference from a cross-flow fan in a variable frequency air conditioner according to claim 3, characterized in that, In the source harmonic reduction step, the lowest windshield operating speed is 820 r / min, the first threshold is 750 r / min, and the second threshold is 720 r / min.

5. The method for suppressing resonant conducted interference from a variable frequency air conditioner cross-flow fan according to claim 1, characterized in that, In the resonant frequency band offset step, the target frequency is in the range of 15kHz to 18kHz and is offset from the system's torsional inherent resonant frequency by at least 2kHz.

6. The method for suppressing resonant conducted interference from a cross-flow fan in a variable frequency air conditioner according to claim 5, characterized in that, In the resonant frequency band misalignment step, when the fan diameter reaches 108mm, the preset frequency is 20kHz and the target frequency is 16kHz.

7. The method for suppressing resonant conducted interference from a cross-flow fan in a variable frequency air conditioner according to claim 1, characterized in that, In operation a) of the path isolation and blocking step, the predetermined spacing is not less than 5mm.

8. The method for suppressing resonant conducted interference from a cross-flow fan in a variable frequency air conditioner according to claim 1, characterized in that, The path isolation and blocking step further includes: adding a fixed point on the wiring path of the motor cable of the fan motor to constrain the motor cable to maintain a non-contact state with other wiring in the unit.

9. A variable frequency air conditioner, comprising an indoor unit, the indoor unit having a cross-flow fan, a fan motor, an electrical control box, an electric heater, and a motor controller, characterized in that: The portion of the electric heating wire extending outside the electrical control box is folded back and fixed inside the electrical control box, and there is a predetermined distance between the electric heating wire and the fan motor housing; The motor cable of the fan motor is routed along an independent path, keeping it in a non-contact state with other connections in the unit, and fixed points are set along the wiring path of the motor cable to maintain the non-contact state. The motor controller is configured to perform the method of any one of claims 1 to 8.

10. The variable frequency air conditioner according to claim 9, characterized in that, The predetermined distance between the electric heating wire and the fan motor housing is not less than 5mm.

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