Electromagnetic heating control system and air conditioner

Abstract

The invention discloses an electromagnetic heating control system and an air conditioner, the electromagnetic heating control system comprises a frequency conversion topology circuit structure, the frequency conversion topology circuit structure comprises an inversion unit, and the phase angle corresponding to the interval of the PWM count of a triangular carrier between zero and a PWM period set value is 60 degrees; the control adjusting module is used for adjusting the duty ratio of two phases of PWM to be different from the duty ratio of the rest phase of PWM when the alternating current motor driven by the inversion unit needs to be heated, so that the phase difference between the two phases of PWM is 120 degrees, the phase difference between one phase of PWM and the rest phase of PWM is larger than 120 degrees, and the phase difference between the other phase of PWM and the rest phase of PWM is larger than 120 degrees; and the phase difference between the other phase of PWM and the rest phase of PWM is less than 120 degrees. According to the invention, by adjusting the PWM comparison value of two adjacent phases, the direct current bias is superposed to the three-phase alternating current, so that the effective electromagnetic heating of the motor is realized.

Description

An electromagnetic heating control system and an air conditioner Technical Field

[0001] This invention relates to the field of electromagnetic heating technology, and in particular to an electromagnetic heating control system and an air conditioner. Background Technology

[0002] In recent years, the demand for air conditioners has been expanding across various regions, especially in northern areas where air conditioners are used for heating in low winter temperatures. In an air conditioning system, the compressor acts as the power unit, and the viscosity of the refrigerant oil inside the compressor plays a crucial role in its reliability. When the outdoor unit is powered off and left stagnant for an extended period in low outdoor temperatures, due to the miscibility of the lubricating oil and refrigerant, a large amount of refrigerant will accumulate in the compressor crankcase. This leads to a decrease in lubricating oil concentration, failing to meet the compressor's lubrication requirements. Insufficient lubrication hinders the air conditioning system's startup, and the extremely low temperature of motor components at low temperatures can also cause unreliable starting.

[0003] To avoid damaging the compressor, it is necessary to preheat the compressor before starting it to ensure that the lubricating oil meets reliability requirements after the compressor starts.

[0004] Currently, most industries use auxiliary heating, which involves installing an electric heating element inside the compressor or placing it on the outer wall of the compressor cylinder. Before the air conditioner compressor is turned on, the oil sump is preheated by the electric heating element. The compressor is then turned on after the control conditions are met. This increases the overall cost of the machine, results in high heat loss, high energy consumption, low heating efficiency, and a long preheating cycle.

[0005] The information disclosed in this background section is only intended to enhance the understanding of the background technology of this application, and therefore may include prior art that is not known to those skilled in the art. Summary of the Invention

[0006] In view of the problems pointed out in the background art, the present invention provides an electromagnetic heating control system that achieves electromagnetic heating of the motor windings by applying an AC current biased by a DC current to the motor windings, and can meet the heating needs of different motors.

[0007] To achieve the above-mentioned objectives, the present invention employs the following technical solution: In some embodiments of this application, an electromagnetic heating control system is provided, comprising: a frequency conversion topology circuit structure, including an inverter unit, a triangular carrier wave comparing a PWM comparison value and outputting a three-phase PWM for controlling the switching transistors in the inverter unit, wherein the phase angle corresponding to the PWM count of the triangular carrier wave between zero and a PWM period set value is 60 degrees; a control adjustment module, configured to, when heating an AC motor driven by the inverter unit is required, adjust the duty cycle of two phase PWMs to be different from the duty cycle of the remaining phase PWM, such that the phase difference between the two phase PWMs is 120 degrees, the phase difference between one phase PWM and the remaining phase PWM is greater than 120 degrees, and the phase difference between the other phase PWM and the remaining phase PWM is less than 120 degrees; wherein, before adjustment, the period of each phase PWM is three times the PWM period.

[0008] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: by adjusting the comparison value of two-phase PWM, the duty cycle of two-phase PWM is adjusted, so that the rising edge of the high level of the three-phase PWM no longer maintains a 120-degree relationship, thereby forming a DC current bias, and then electromagnetically heating the motor windings to improve the heating effect, which is particularly suitable for small compressors with large resistance.

[0009] Furthermore, by adjusting the duty cycle of the two-phase PWM, the magnitude of the DC current component can be changed to meet the different heating requirements of various types of AC motors.

[0010] In some embodiments of this application, the control adjustment module adjusts the duty cycle of two of the PWM phases to be different from the duty cycle of the remaining PWM phase. Specifically, for the triangular carrier corresponding to the high level of each of the three PWM phases, the comparison value of two of the PWM phases is adjusted from zero to a non-zero value, so that the output position of the high level rising edge of the two PWM phases is shifted backward by angle α1 or forward by angle α2, or the output position of the high level falling edge of the two PWM phases is shifted forward by angle α3 or backward by angle α4.

[0011] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: by changing the comparison value of the two-phase PWM, the offset of the high-level pulse width of the two-phase PWM is realized, thereby adjusting the duty cycle of the two-phase PWM to achieve the control of the DC current component.

[0012] In some embodiments of this application, the control adjustment module is further configured to: acquire the actual DC current component; increase or decrease the offset angle according to the instruction value corresponding to the DC current component instruction and the actual DC current component, so that the actual DC current component is equal to the DC current component.

[0013] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: by adjusting the duty cycle of the two-phase PWM according to the instruction value corresponding to the DC current component instruction, the DC current component can be adjusted to meet the different heating requirements of different AC motors using electromagnetic heating.

[0014] In some embodiments of this application, the high-level rising edge output positions of the two PWM phases are offset backward by an angle α1. Specifically: during the PWM count increment phase, when the PMW comparison value is adjusted to be greater than zero and less than the PWM count setting value, the high-level rising edge output positions of the two PWM phases are offset backward by an angle α1 greater than zero and less than 60 degrees; when the PWM count increments and the PMW comparison value reaches the PWM count setting value, the high-level rising edge output positions of the two PWM phases are offset backward by an angle α1 equal to 60 degrees; during the PWM count decrement phase, when the PMW comparison value is adjusted to be greater than zero and less than the PWM count setting value, the high-level rising edge output positions of the two PWM phases are offset backward by an angle α1 greater than 60 degrees and less than 120 degrees.

[0015] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: depending on the different comparison values ​​of a certain phase PWM, the high level of the phase PWM has different angles, thereby realizing different magnitude control of the DC current component.

[0016] In some embodiments of this application, the control adjustment module is further configured to: cyclically switch the combined phase sequence of two adjacent phases in a three-phase PWM for duty cycle adjustment.

[0017] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: by cyclically switching the combination phase sequence of two adjacent phases in the three-phase PWM used for bias pulse regulation, the switching transistors in the inverter unit can be heated evenly, thereby improving the reliability of the motor.

[0018] In some embodiments of this application, the control adjustment module switches the combined phase sequence by determining whether the heat generated by the three-phase motor windings exceeds a set heat generated.

[0019] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: the heat generation of the three-phase motor windings can measure the preheating required by the motor. Therefore, the combination phase sequence of two adjacent phases in the phase PWM can be adjusted according to the heat generation to ensure the reliability of the switching transistors in the inverter unit while meeting the preheating requirements.

[0020] In some embodiments of this application, the phase sequence is switched by determining whether the heat generation of the three-phase motor winding exceeds a set heat generation value. Specifically: S1: During the duty cycle adjustment of the two-phase PWM corresponding to the first phase sequence, the heat generation of the three-phase motor winding is calculated; S2: When the heat generation of the three-phase motor winding exceeds the set heat generation value, the first phase sequence is switched to the second phase sequence; S3: During the duty cycle adjustment of the two-phase PWM corresponding to the second phase sequence, the heat generation of the three-phase motor winding is calculated; S4: When the heat generation of the three-phase motor winding exceeds the set heat generation value, the second phase sequence is switched to the third phase sequence; S5: During the duty cycle adjustment of the two-phase PWM corresponding to the third phase sequence, the heat generation of the three-phase motor winding is calculated; S6: When the heat generation of the three-phase motor winding exceeds the set heat generation value, the third phase sequence is switched back to the first phase sequence, and the process returns to S1.

[0021] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: the heat generation of the three-phase motor windings is used to measure the preheating required by the motor. Therefore, the combination phase sequence of two adjacent phases in the phase PWM can be adjusted according to the heat generation, so as to ensure the reliability of the switching transistors in the inverter unit while meeting the preheating requirements.

[0022] In some embodiments of this application, an electromagnetic heating control system is characterized by comprising: a frequency conversion topology circuit structure, including an inverter unit, wherein a triangular carrier wave is compared with a PWM comparison value and outputs a three-phase PWM for controlling the switching transistors in the inverter unit, wherein the phase angle corresponding to the PWM count of the triangular carrier wave between zero and a PWM period set value is 60 degrees; a control adjustment module, configured to execute a first DC bias mode and a second DC bias mode when heating of an AC motor driven by the inverter unit is required; in the first DC bias mode, adjusting the duty cycle of a certain phase PWM to be different from the duty cycles of the remaining two phase PWMs, such that the phase difference between the remaining two phase PWMs is 120 degrees, and the phase difference between one of the remaining two phase PWMs and the first phase PWM is greater than 120 degrees. The phase difference between the other phase PWM and the first phase PWM is less than 120 degrees. In the second DC bias mode, the duty cycle of two of the PWMs is adjusted to be different from the duty cycle of the remaining PWM, so that the phase difference between the two PWMs is 120 degrees, the phase difference between the one PWM and the remaining PWM is greater than 120 degrees, and the phase difference between the other PWM and the remaining PWM is less than 120 degrees. The control adjustment module is also configured to: cyclically switch the phase sequence of the three-phase PWMs with duty cycle adjustment in the first DC bias mode and the combined phase sequence of the two-phase PWMs with duty cycle adjustment in the second DC bias mode. The period of each PWM before adjustment is three times the PWM period.

[0023] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: The electromagnetic heating control system involved in this application can increase the DC bias current on the basis of the original AC current component to realize electromagnetic heating, improve the electromagnetic heating effect, and meet the heating needs of various types of motors. In addition, the path of the total DC bias current flowing through the switching transistor in the inverter unit in the first DC bias mode is different from the path of the total DC bias current flowing through the switch in the second DC bias mode. The PWM phase sequence of each phase with the duty cycle is cyclically switched to change the switching transistor through which the total DC bias current flows, ensuring uniform stress and balanced heating on the switching transistor in the inverter unit, and extending the service life of the inverter unit.

[0024] In some embodiments of this application, an air conditioner is also disclosed, comprising: a refrigerant circulation loop for circulating refrigerant in a compressor, condenser, expansion valve, and evaporator; the compressor being driven by a motor for compressing low-temperature, low-pressure refrigerant gas into high-temperature, high-pressure refrigerant gas and discharging it to the condenser; and a variable frequency topology circuit structure including an inverter unit, wherein a triangular carrier wave is compared with a PWM comparison value and outputs a three-phase PWM for controlling the switching transistors in the inverter unit, wherein the phase angle corresponding to the PWM count of the triangular carrier wave between zero and the PWM period set value is 6°. 0 degrees; The control adjustment module, configured to adjust the duty cycle of two phase PWMs to be different from the duty cycle of the remaining phase PWM when heating of the AC motor driven by the inverter unit is required, such that the phase difference between the two phase PWMs is 120 degrees, the phase difference between one phase PWM and the remaining phase PWM is greater than 120 degrees, and the phase difference between the other phase PWM and the remaining phase PWM is less than 120 degrees; wherein, before adjustment, the period of each phase PWM is three times the PWM period.

[0025] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: Some embodiments of this application involve air conditioners that adjust the duty cycle of the two adjacent phase PWMs by adjusting the PWM comparison value corresponding to the two adjacent phase PWMs, thereby controlling the magnitude of the DC current component.

[0026] An electromagnetic heating control system is used to preheat the compressor electromagnetically before it starts, thereby heating the oil sump and ensuring that the compressor starts normally after the preheating stage is completed.

[0027] Other features and advantages of the present invention will become clearer after reading the detailed embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 is a circuit diagram of an existing frequency converter topology; Figure 2 is a schematic diagram of PWM generation; Figure 3 is a waveform diagram of the original three-phase PWM generated according to the embodiment; Figure 4 is a waveform diagram of the three-phase PWM generated according to the embodiment (first waveform); Figure 5 is a waveform diagram of the three-phase PWM generated according to the embodiment (second waveform); Figure 6 is a waveform diagram of the three-phase PWM generated according to the embodiment (third waveform); Figure 7 is a waveform diagram of the three-phase PWM generated according to the embodiment (fourth waveform); Figure 8 is a waveform diagram of the U-phase current before and after adjusting the AC current component according to the embodiment; Figure 9 is a schematic diagram of the duty cycle adjustment of the V-phase PWM according to the embodiment; Figure 10 is a diagram of the duty cycle adjustment of the V-phase PWM in Figure 9. Figure 11 is a schematic diagram of the DC bias current path in the inverter topology circuit structure according to the embodiment, in which the AC current component is adjusted; Figure 12 is a schematic diagram of the DC bias current path in the inverter topology circuit structure when the duty cycle of the V-phase PWM and W-phase PWM is adjusted according to the embodiment; Figure 13 is a schematic diagram of the control of the inverter unit by the electromagnetic control system according to the embodiment; Figure 14 is a schematic diagram of the duty cycle adjustment of the V-phase PWM and W-phase PWM according to the embodiment, in which the AC current component is not adjusted; Reference numerals: 10, AC motor; 20, inverter unit. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. A frequency conversion topology circuit structure is used to perform frequency conversion control on a motor (e.g., a permanent magnet synchronous motor, an AC motor).

[0031] The compressor motor in an air conditioner is generally an AC motor. Therefore, the variable frequency topology circuit structure is widely used in air conditioners to adjust the frequency of the compressor motor in the air conditioner.

[0032] See Figure 1, which shows the structure of the frequency converter topology circuit.

[0033] In some embodiments of this application, the frequency conversion topology circuit structure includes a rectifier unit (not shown) and an inverter unit 20.

[0034] The input terminal of the rectifier unit is connected to the AC power supply. The rectifier unit is used to rectify the AC power supplied by the AC power supply to obtain rectified DC power.

[0035] Inverter unit 20 receives rectified DC power and inverts it into three-phase AC power for use by AC motor 10.

[0036] The rectifier unit can be a single-phase rectifier bridge, which is formed by connecting four rectifier diodes in series.

[0037] Inverter unit 20 is a three-phase power inverter used to invert DC power to drive AC motor 10.

[0038] The three-phase power inverter consists of six switching transistors: T1 for the upper arm of phase U, T3 for the upper arm of phase V, T5 for the upper arm of phase W, T2 for the lower arm of phase U, T4 for the lower arm of phase V, and T6 for the lower arm of phase W.

[0039] The triangular carrier wave is compared with the PWM comparison value and the PWM is output to control the switching transistors in the inverter unit 20.

[0040] The above-described frequency converter topology is merely an example, and the frequency converter topology involved in this application is not limited to the above.

[0041] Variable frequency topology circuits are mostly used in air conditioner outdoor units. This application is concerned with preheating control before the motor starts.

[0042] Electromagnetic heating control system Electromagnetic heating, as a highly efficient heating method, is not only widely used in the field of kitchen appliances, but also for starting the compressor in the outdoor unit of an air conditioner under low ambient temperature.

[0043] First, refer to Figure 2, which illustrates the principle of PWM generation.

[0044] The PWM counting method of the triangular carrier uses an up-down counting mode. That is, it starts counting from the zero value at the trough of the triangular carrier and increases the count until the peak reaches the PWM period set value N. Then it starts counting from the peak back to the zero value at the trough, and so on.

[0045] The time period during which the PWM count increases from zero to the PWM period set value and then decreases back to zero is the carrier period Ts (i.e., the PWM period).

[0046] When the PWM count value is less than the PWM comparison value, the PWM output is low; when the PWM count value is greater than the PWM comparison value, the PWM output is high.

[0047] When the PWM comparison value is the PWM period setting value, the PWM output is always low.

[0048] When the PWM compare value is zero, the PWM output remains high.

[0049] In some embodiments of this application, the period of the three-phase PWM (i.e., U phase, V phase and W phase) of the motor is first set to three times the PWM period (i.e. the carrier period of the triangular carrier), see Figure 3.

[0050] Divide each half-cycle of the PWM into an interval. Thus, the cycle of the three-phase PWM corresponds to six intervals: S1, S2, S3, S4, S5, and S6. Therefore, each interval is 1 / 6 of the cycle of the three-phase PWM (360 degrees), which is 60 degrees.

[0051] That is, when the PWM count value increases from zero to the PWM period set value, it is a range, and the corresponding phase angle is 60 degrees. When the PWM count value decreases from the PWM period set value to zero, it is also a range, and the corresponding phase angle is also 60 degrees.

[0052] Referring to Figure 3, before the three-phase PWM is adjusted, the rising phase of the high level of the three-phase PWM is 120 degrees apart, the duty cycle of each phase PWM is 50%, and the phase difference between the PWM comparison values ​​of each phase used for modulation is also 120 degrees.

[0053] Using the three-phase PWM control shown in Figure 3, the inverter unit 20 in Figure 1 generates a three-phase voltage for the motor. After the voltage is applied to the motor windings, a three-phase AC current is formed. This three-phase AC current is an AC current without added DC bias and without adjustment of the AC current component.

[0054] Pure AC heating is a type of electromagnetic heating. For compressors with small winding inductance and resistance, the AC current component is relatively large. However, the current technology cannot adjust the magnitude of the AC current component, resulting in poor control accuracy of the heating effect.

[0055] In some embodiments of this application, it is necessary to simultaneously adjust the PWM comparison value of each phase PWM to simultaneously adjust the duty cycle of the three-phase PWM, so that the duty cycle of each phase PWM changes equally (equally increases or equal decreases), and the phase difference between the rising edges of the high level of the three-phase PWM is maintained at 120 degrees, so as to realize the control of the AC current component, improve the electromagnetic heating effect, realize the electromagnetic heating control of the motor before the motor starts, thereby ensuring the preheating of the motor under low ambient temperature so as to reliably start the motor.

[0056] In some embodiments of this application, the electromagnetic heating involved is AC heating, and the AC current component is used for control purposes, which can flexibly control the AC current component and ensure the electromagnetic heating effect.

[0057] In some embodiments of this application, the electromagnetic control system also relates to a control adjustment module (not shown) for simultaneously adjusting the duty cycle of each phase of the three-phase PWM.

[0058] Among them, adjusting the PWM duty cycle of each phase includes adjusting to increase the PWM duty cycle of each phase and adjusting to decrease the PWM duty cycle of each phase.

[0059] The control adjustment module adjusts the PWM comparison value corresponding to the high level of each phase PWM, adjusts the PWM comparison value from zero to a non-zero value, and makes the high level of the corresponding phase PWM generate a bias angle.

[0060] In some embodiments of the present application, when the rising edge of the high level of the corresponding phase PWM is shifted backward by an angle α1 or the falling edge of the high level of the corresponding phase PWM is shifted forward by an angle α3, the PWM duty cycle of each phase is reduced.

[0061] In some embodiments of the present application, when the rising edge of the high level of the corresponding phase PWM is shifted forward by an angle α3 or the falling edge of the high level of the corresponding phase PWM is shifted backward by an angle α4, the PWM duty cycle of each phase is increased.

[0062] In some embodiments of the present application, referring to FIGS. 4 and 5, which show the schematic diagram of reducing the duty cycle of each phase PWM.

[0063] In some embodiments of the present application, in combination with FIGS. 3 and 4, in the S1 interval, the PWM comparison value of the U phase is no longer zero, but is offset by a certain value △n (0 < △n < PWM cycle setting value), then the output position of the rising edge of the high level of the U phase PWM is shifted backward by an angle α1 compared to the position shown in FIG. 3.

[0064] Similarly, in the S3 interval, the PWM comparison value of the V phase is also no longer zero, and is also offset by a certain value △n, then the output position of the rising edge of the high level of the V phase PWM is shifted backward by an angle α1 compared to the position shown in FIG. 3; in the S5 interval, the PWM comparison value of the W phase is also no longer zero, and is also offset by a certain value △n, then the output position of the rising edge of the high level of the W phase PWM is shifted backward by an angle α compared to the position shown in FIG. 3.

[0065] Above, the phase difference of the rising edges of the high levels of the three-phase PWM is still 120 degrees, without a DC bias component, but the PWM duty cycle of each phase becomes smaller, that is, this adjustment method reduces the AC current component.

[0066] In some embodiments of the present application, still referring to FIG. 4, taking the U phase PWM as an example, as the PWM comparison value of the U phase increases to the PWM cycle setting value, or is no longer zero in the S2 interval, at this time, the output position of the rising edge of the high level of the U phase PWM is shifted backward by an angle greater than α1 compared to the position shown in FIG. 3, that is, the AC current component is further reduced. <Q

[0067] Similarly, the V phase PWM and the W phase PWM also perform the same corresponding PWM comparison value setting as above.

[0068] In some embodiments of the present application, with reference to FIGS. 3 and 5, taking the adjustment of the U-phase PWM duty cycle as an example, in the S3 interval, the U-phase PWM comparison value is no longer zero, but is offset by a certain value PWM cycle set value - △n (0 < △n < PWM cycle set value), then the output position of the falling edge of the U-phase PWM high level is shifted forward by an angle α3 compared to the position shown in FIG. 3.

[0069] Similarly, in the S5 interval, the V-phase PWM comparison value is also no longer zero, and is also offset by a certain value PWM cycle set value - △n, then the output position of the falling edge of the V-phase PWM high level is shifted forward by an angle α3 compared to the position shown in FIG. 3; in the S1 interval of the next three-phase PWM cycle, the W-phase PWM comparison value is also no longer zero, and is also offset by a certain value PWM cycle set value - △n, then the output position of the falling edge of the W-phase PWM high level is shifted forward by an angle α3 compared to the position shown in FIG. 3.

[0070] As above, the phase difference of the falling edges of the three-phase PWM high levels is still 120 degrees, without a DC offset component, but the PWM duty cycle of each phase also becomes smaller, that is, this adjustment method also reduces the AC current component.

[0071] It should be noted that when adjusting the duty cycle of each phase PWM, the offset angle of each phase PWM is the same, that is, the duty cycle of the corresponding phase PWM after adjustment is the same.

[0072] In some embodiments of the present application, referring to FIGS. 6 and 7, which show the schematic diagram of increasing the duty cycle of each phase PWM.

[0073] In some embodiments of the present application, with reference to FIGS. 3 and 6, taking the adjustment of the U-phase PWM duty cycle as an example, in the S6 interval of the previous three-phase PWM cycle, the U-phase PWM comparison value is no longer zero, but is offset by a certain value △n (0 < △n < PWM cycle set value), then the output position of the rising edge of the U-phase PWM high level is shifted forward by an angle α2 compared to the position shown in FIG. 3.

[0074] Similarly, in the S2 interval, the V-phase PWM comparison value is also no longer zero, and is also offset by a certain value △n, then the output position of the rising edge of the V-phase PWM high level is shifted forward by an angle α2 compared to the position shown in FIG. 3; in the S4 interval, the W-phase PWM comparison value is also no longer zero, and is also offset by a certain value △n, then the output position of the rising edge of the W-phase PWM high level is shifted forward by an angle α2 compared to the position shown in FIG. 3.

[0075] As above, the phase difference of the rising edges of the three-phase PWM high levels is still 12 degrees, without a DC offset component, but the PWM duty cycle of each phase increases, that is, this adjustment method also increases the AC current component.

[0076] In some embodiments of the present application, with reference to FIGS. 3 and 7, taking the adjustment of the U-phase PWM duty cycle as an example, in the S4 interval, the U-phase PWM comparison value is no longer zero, but is offset by a certain value PWM cycle setting value - △n (0 < △n < PWM cycle setting value), then the output position of the falling edge of the U-phase PWM high level is shifted backward by an angle α4 compared to the position shown in FIG. 3.

[0077] Similarly, in the S6 interval, the V-phase PWM comparison value is also no longer zero, and is also offset by a certain value PWM cycle setting value - △n, then the output position of the falling edge of the V-phase PWM high level is shifted backward by an angle α4 compared to the position shown in FIG. 3; in the S2 interval of the next three-phase PWM cycle, the W-phase PWM comparison value is also no longer zero, and is also offset by a certain value PWM cycle setting value - △n, then the output position of the falling edge of the W-phase PWM high level is shifted backward by an angle α compared to the position shown in FIG. 3.

[0078] As above, the phase difference of the rising edges of the three-phase PWM high levels is still 120 degrees, without a DC offset component, but the duty cycle of each phase PWM also increases, that is, this adjustment method also increases the AC current component.

[0079] As described above, the adjustment of the AC current component can be achieved by controlling the duty cycle of each phase PWM.

[0080] Referring to FIG. 8, it shows a schematic diagram of the current comparison before and after the adjustment of the AC current component.

[0081] The dash line i1 represents the U-phase AC current obtained by increasing the AC current component, and the solid line i2 represents the U-phase AC current obtained by decreasing the AC current component.

[0082] In some embodiments of the present application, in order to implement closed-loop control of the AC current component, it is necessary to sample the peak value of the AC current.

[0083] Referring to FIGS. 4 to 7, it shows the sampling positions of the minimum value and the maximum value of the U-phase current.

[0084] In some embodiments of the present application, since the motor winding is an inductive load, when the PWM level of a certain phase changes, the current in the winding of that phase reaches the peak value and turns, the winding current reaches the minimum value and starts to increase from small to large at the PWM rising edge, and the winding current reaches the maximum value and starts to decrease from large to small at the PWM falling edge. Therefore, the sampling points should be set at the rising edge and the falling edge of the PWM. <o000175>

[0085] However, since the PWM level change will cause current ringing, resulting in distortion when sampling the current at the PWM rising edge and falling edge, the sampling points should be arranged before the PWM rising edge and falling edge and close to the rising edge and falling edge. <o000178>In some embodiments of this application, taking the U-phase current as an example, the minimum value sampling point is located at the position of the difference between the PWM count corresponding to the rising edge of the U-phase PWM high level and the first time period on the triangular carrier wave. The first time period can be set and should be as small as possible. The maximum value sampling point is located at the position of the difference between the PWM count corresponding to the falling edge of the U-phase PWM high level and the second time period on the triangular carrier wave. The second time period can be set and should be as small as possible.

[0087] In some embodiments of this application, considering the dead time Td and the AD sampling time Tad, taking the U-phase current as an example, as shown in Figure 4, the minimum sampling point is set at Δn-β1, where β1=Td+Tad, and the maximum sampling point is set at the PWM period setting value-β2, where β2=Tad.

[0088] The minimum and maximum sampling points in Figures 5 to 7 were also obtained in a similar manner to that shown in Figure 4, and will not be repeated here.

[0089] In some embodiments of this application, since pure AC heating has no DC component, the AC current component is small for compressors with large winding inductance and resistance, resulting in poor heating effect. Therefore, in some embodiments of this application, a DC bias current is superimposed on the AC current component to improve the electromagnetic heating effect.

[0090] In some embodiments of this application, the control adjustment module may be configured to execute a first DC bias mode to superimpose a DC bias current onto the AC current component.

[0091] In some embodiments of this application, in the first DC bias mode, the control adjustment module is also used to adjust the duty cycle of a certain phase PWM to be different from the duty cycles of the remaining two phase PWMs, and to adjust the high-level duty cycle of the certain phase PWM so that the phase difference between the three phase PWMs no longer remains at 120 degrees, thereby generating a DC bias current and realizing electromagnetic heating control of the motor windings.

[0092] Adjusting the duty cycle of a certain phase PWM includes increasing the duty cycle of a certain phase PWM and decreasing the duty cycle of a certain phase PWM.

[0093] The control adjustment module adjusts the PWM comparison value corresponding to the high level of a certain phase PWM, changing the PWM comparison value from zero to a non-zero value, thereby causing the high level of that phase PWM to have an offset angle.

[0094] The larger the offset angle γ, the greater the preheating heat.

[0095] In some embodiments of this application, see Figure 9, which illustrates the generation of a V-phase DC bias current.

[0096] Referring to Figure 4, when the rising edge of the high level of each phase PWM is offset backward by an angle α1, the PWM comparison value corresponding to the V phase PWM can be adjusted so that the output position of the rising edge of the high level of the V phase PWM is offset backward by an angle γ1. This results in a phase difference of 120 degrees + γ1 between the rising edge of the high level of the V phase PWM and the rising edge of the high level of the U phase PWM, a phase difference of 120 degrees - γ1 between the rising edge of the high level of the W phase PWM and the rising edge of the high level of the V phase PWM, and a phase difference of 120 degrees between the rising edge of the high level of the W phase PWM and the rising edge of the high level of the U phase PWM.

[0097] Since the phase difference of the three-phase PWM is no longer maintained at 120 degrees, a DC bias current is generated.

[0098] Referring to Figure 10, the DC bias current passes through the switch T3 of the upper arm of phase V, and flows into the switch T2 of the lower arm of phase U and the switch T6 of the lower arm of phase W in inverter unit 20, respectively, and then flows out. That is, the total DC bias current flows through the switch T3 of the upper arm of phase V.

[0099] Similarly, the phase sequence of the three-phase PWM can be changed to generate a U-phase DC bias current or a W-phase DC bias current.

[0100] When the U-phase DC bias current is generated, the DC bias current passes through the switch T1 of the upper bridge arm of the U-phase and flows into the switch T4 of the lower bridge arm of the V-phase and the switch T6 of the lower bridge arm of the W-phase in the inverter unit 20, and then flows out. That is, the total DC bias current flows through the switch T1 of the upper bridge arm of the U-phase.

[0101] When the DC bias current of phase W is generated, the DC bias current passes through the switch T5 of the upper bridge arm of phase W and flows into the switch T2 of the lower bridge arm of phase U and the switch T6 of the lower bridge arm of phase V in inverter unit 20, and then flows out. That is, the total DC bias current flows through the switch T5 of the upper bridge arm of phase W.

[0102] In some embodiments of this application, the generation of V-phase DC bias current is still used as an example for illustration.

[0103] Referring to Figure 5, when the output position of the high-level falling edge of each phase PWM is shifted forward by an angle α3, the PWM comparison value corresponding to the V-phase PWM can be adjusted to shift the output position of the high-level falling edge of the V-phase PWM forward by an angle γ3. This results in a phase difference of 120 degrees + γ3 between the high-level falling edge of the V-phase PWM and the high-level falling edge of the W-phase PWM, a phase difference of 120 degrees between the high-level falling edge of the W-phase PWM and the high-level falling edge of the U-phase PWM, and a phase difference of 120 degrees - γ3 between the high-level falling edge of the U-phase PWM and the high-level falling edge of the V-phase PWM, thus generating a DC bias.

[0104] Similarly, the phase sequence of the three-phase PWM can be changed to generate a U-phase DC bias current or a W-phase DC bias current.

[0105] In some embodiments of this application, when the output position of the rising edge of the high level of each phase PWM is shifted forward by an angle α2, the PWM comparison value corresponding to the V phase PWM can be adjusted so that the output position of the rising edge of the high level of the V phase PWM is shifted forward by an angle γ2.

[0106] At this time, the rising edge of the high level of the V-phase PWM is 120 degrees + γ2 out of phase with the rising edge of the high level of the W-phase PWM, the rising edge of the high level of the W-phase PWM is 120 degrees out of phase with the rising edge of the high level of the U-phase PWM, and the falling edge of the high level of the U-phase PWM is 120 degrees - γ2 out of phase with the rising edge of the high level of the V-phase PWM, thus generating DC bias.

[0107] Similarly, the phase sequence of the three-phase PWM can be changed to generate a U-phase DC bias current or a W-phase DC bias current.

[0108] In some embodiments of this application, when the output position of each phase PWM high level falling edge is shifted backward by angle α4, the PWM comparison value corresponding to the V phase PWM can be adjusted so that the output position of the V phase PWM high level falling edge is shifted backward by angle γ4.

[0109] At this time, the falling edge of the high level of the V-phase PWM is 120 degrees - γ4 out of phase with the falling edge of the high level of the W-phase PWM, the falling edge of the high level of the W-phase PWM is 120 degrees out of phase with the falling edge of the high level of the U-phase PWM, and the falling edge of the high level of the U-phase PWM is 120 degrees + γ4 out of phase with the falling edge of the high level of the V-phase PWM, thus generating DC bias.

[0110] Similarly, the phase sequence of the three-phase PWM can be changed to generate a U-phase DC bias current or a W-phase DC bias current.

[0111] The current sampling point method applicable to the control of the AC current component as described above is still suitable for using dual closed-loop control of the current sampling points of both the AC and DC current components.

[0112] Therefore, the actual DC current component is iu+(-iu)≠0.

[0113] In some embodiments of this application, a direct current component command can be given, and the preheating control can be achieved by controlling the magnitude of the direct current component.

[0114] The actual collected DC current component is compared with the command value of the DC current component command.

[0115] If the actual DC current component is less than the command value of the DC current component command, a larger offset angle γ is formed, generating a larger actual DC current component; conversely, it is reduced until the command value requirement of the DC current component command is met.

[0116] The electromagnetic heating control system described above, as shown in Figure 13, includes a first single closed loop that controls the AC current component and a second single closed loop that controls the DC current component generated using a first DC bias mode. The outputs of the first and second single closed loops can be superimposed by an adder to drive the switching transistors of the inverter unit 20.

[0117] In Figure 13, the duty cycle of a certain phase PWM in the second single closed loop refers to the duty cycle of the biased three-phase PWM.

[0118] When in use, you can choose to use an independent first single closed loop, a second single closed loop, or a dual closed loop system with a first single closed loop and a second single closed loop to control the AC current component and the DC current component, depending on the actual needs, so as to meet various electromagnetic control requirements and ensure heating effect.

[0119] In the first DC bias mode as described above, the total DC bias current flows through the upper bridge switch of a certain phase.

[0120] As described above, when using dual closed-loop control of AC and DC current components, in order to ensure uniform heating of each phase winding during preheating, the control adjustment module can be configured to perform cyclic switching of the three-phase PWM phase sequence for duty cycle adjustment in the first DC bias.

[0121] For example, when superimposing DC bias, referring to Figure 9, the rising edge of the high level of the V phase PWM is first shifted backward by an angle γ1, and after a period of time, the rising edge of the high level of the W phase PWM is shifted backward by an angle γ1. After a period of time, the rising edge of the high level of the U phase PWM is shifted backward by an angle γ1. This cycle is repeated so that the total DC bias current flows sequentially through the switch T3 of the upper bridge arm of the V phase, the switch T5 of the upper bridge arm of the W phase, and the switch T1 of the upper bridge arm of the U phase, thereby achieving uniform thermal stress on the switches of the inverter unit 20.

[0122] In some embodiments of this application, when switching to adjust the duty cycle of a certain phase PWM, the phase sequence can be switched by determining whether the heat generation exceeds the set heat generation.

[0123] The heat generation of the three-phase motor windings is calculated during the adjustment of the duty cycle of the U-phase PWM.

[0124] When the heat generated by the three-phase motor windings exceeds the set heat generation, the phase sequence of the three-phase PWM is switched to adjust the duty cycle of the V-phase PWM.

[0125] The heat generation of the three-phase motor windings is calculated during the adjustment of the duty cycle of the V-phase PWM signal.

[0126] When the heat generated by the three-phase motor windings exceeds the set heat generation, the phase sequence of the three-phase PWM is switched to adjust the duty cycle of the W-phase PWM.

[0127] The heat generation of the three-phase motor windings is calculated during the adjustment of the duty cycle of the W-phase PWM.

[0128] When the heat generated by the three-phase motor windings exceeds the set heat generation, the phase sequence of the three-phase PWM is switched to adjust the duty cycle of the U-phase PWM.

[0129] During the adjustment of the duty cycle of one phase PWM, when the heat generated by the winding exceeds the set heat generation, the phase sequence of the three-phase PWM is switched to avoid uneven heating of the three-phase motor windings and ensure the safety of the three-phase motor.

[0130] In some embodiments of this application, the phase sequence can also be switched by setting a duration.

[0131] In some embodiments of this application, the control adjustment module may be configured to execute a second DC bias mode to superimpose a DC bias current onto the AC current component.

[0132] In some embodiments of this application, in the second DC bias mode, the control adjustment module is also used to adjust the duty cycle of two phase PWMs to be different from the duty cycle of the remaining phase PWM, and to adjust the high-level duty cycle of two phase PWMs so that the phase difference between the three phase PWMs no longer remains at 120 degrees, thereby generating a DC bias current and realizing electromagnetic heating control of the motor windings.

[0133] Adjusting the duty cycle of a two-phase PWM includes both increasing the duty cycle of the two-phase PWM and decreasing the duty cycle of the two-phase PWM.

[0134] The control adjustment module adjusts the two-phase PWM comparison value corresponding to the two-phase PWM high level, changing the PWM comparison value from zero to a non-zero value, so that the two-phase PWM high level will generate an offset angle γ.

[0135] The larger the offset angle γ, the greater the preheating heat.

[0136] In some embodiments of this application, referring to FIG11, the generation of V-phase and W-phase DC bias currents is illustrated as an example.

[0137] Combining Figures 4 and 11, when the rising edge of the high level of each phase PWM is offset backward by an angle α1, the PWM comparison values ​​corresponding to the V-phase PWM and W-phase PWM can be adjusted so that the output position of the rising edge of the high level of the V-phase PWM is offset backward by an angle γ11, and the output position of the rising edge of the high level of the W-phase PWM is also offset backward by an angle γ11.

[0138] At this time, the rising edge of the high level of the V-phase PWM is 120 degrees + γ11 out of phase with the rising edge of the high level of the U-phase PWM, the rising edge of the high level of the W-phase PWM is 120 degrees out of phase with the rising edge of the high level of the V-phase PWM, and the rising edge of the high level of the W-phase PWM is 120 degrees - γ11 out of phase with the rising edge of the high level of the U-phase PWM, thus generating a DC bias current.

[0139] Referring to Figure 12, it shows the DC bias current flow path when DC bias current is generated in phases V and W (indicated by arrows). The DC bias current flows out in parallel through the switch T3 of the upper bridge arm of phase V and the switch T5 of the upper bridge arm of phase W, and then flows into the switch T2 of the lower bridge arm of phase U in inverter unit 20, and then flows out. That is, the total DC bias current flows through the switch T2 of the lower bridge arm of phase U.

[0140] The phase sequence of two phases in a three-phase PWM can be changed to generate DC bias currents for the W and U phases, or DC bias currents for the U and V phases.

[0141] The control generates DC bias currents for phase W and phase U. The DC bias current flows out in parallel through the switch T5 of the upper bridge arm of phase W and the switch T1 of the upper bridge arm of phase U, and then flows into the switch T4 of the lower bridge arm of phase V in inverter unit 20, and then flows out. That is, the total DC bias current flows through the switch T4 of the lower bridge arm of phase V.

[0142] The control generates DC bias currents for phase U and phase V. The DC bias current flows out in parallel through the switch T1 of the upper bridge arm of phase U and the switch T5 of the upper bridge arm of phase V, and then flows into the switch T6 of the lower bridge arm of phase W in inverter unit 20, and then flows out. That is, the total DC bias current flows through the switch T6 of the lower bridge arm of phase W.

[0143] In some embodiments of this application, when the output position of the high-level falling edge of each phase PWM is shifted forward by an angle α3, the PWM comparison values ​​corresponding to the V-phase PWM and the W-phase PWM can be adjusted so that the output position of the high-level falling edge of the V-phase PWM is shifted forward by an angle γ13, and the output position of the high-level falling edge of the W-phase PWM is shifted forward by an angle γ13.

[0144] At this time, the falling edge of the high level of the V-phase PWM and the falling edge of the high level of the W-phase PWM are 120 degrees apart in phase, the falling edge of the high level of the W-phase PWM and the falling edge of the high level of the U-phase PWM are 120 degrees + γ13 apart in phase, and the falling edge of the high level of the U-phase PWM and the falling edge of the high level of the V-phase PWM are 120 degrees - γ3 apart in phase, thus generating DC bias.

[0145] The phase sequence of two phases in a three-phase PWM can be changed to generate DC bias currents for the W and U phases, or DC bias currents for the U and V phases.

[0146] In some embodiments of this application, when the output position of the rising edge of the high level of each phase PWM is shifted forward by an angle α2, the PWM comparison values ​​corresponding to the V-phase PWM and the W-phase PWM can be adjusted so that the output position of the rising edge of the high level of the V-phase PWM is shifted forward by an angle γ12, and the output position of the rising edge of the high level of the W-phase PWM is shifted forward by an angle γ12.

[0147] At this time, the rising edge of the high level of the V-phase PWM and the falling edge of the high level of the W-phase PWM are 120 degrees apart in phase, the rising edge of the high level of the W-phase PWM and the falling edge of the high level of the U-phase PWM are 120 degrees + γ12 apart in phase, and the falling edge of the high level of the U-phase PWM and the falling edge of the high level of the V-phase PWM are 120 degrees - γ12 apart in phase, thus generating DC bias.

[0148] The phase sequence of two phases in a three-phase PWM can be changed to generate DC bias currents for the W and U phases, or DC bias currents for the U and V phases.

[0149] In some embodiments of this application, when the output position of the high-level falling edge of each phase PWM is shifted backward by an angle α4, the PWM comparison values ​​corresponding to the V-phase PWM and the W-phase PWM can be adjusted so that the output position of the high-level falling edge of the V-phase PWM is shifted backward by an angle γ14, and the output position of the high-level falling edge of the W-phase PWM is shifted backward by an angle γ14.

[0150] At this time, the falling edge of the high level of the V-phase PWM and the falling edge of the high level of the W-phase PWM are 120 degrees apart in phase, the falling edge of the high level of the W-phase PWM and the falling edge of the high level of the U-phase PWM are 120 degrees - γ4 apart in phase, and the falling edge of the high level of the U-phase PWM and the falling edge of the high level of the V-phase PWM are 120 degrees + γ4 apart in phase, thus generating DC bias.

[0151] The phase sequence of two phases in a three-phase PWM can be changed to generate DC bias currents for the W and U phases, or DC bias currents for the U and V phases.

[0152] The current sampling point method applicable to the control of the AC current component as described above is still suitable for using dual closed-loop control of the current sampling points of both the AC and DC current components.

[0153] Therefore, the actual DC current component is iu+(-iu)≠0.

[0154] The electromagnetic heating control system described above, still referring to Figure 13, includes a first single closed loop that controls the AC current component and a third single closed loop that controls the DC current component generated using a second DC bias mode. The outputs of the first and third single closed loops can be superimposed by an adder to drive the inverter unit switching transistors.

[0155] In Figure 13, the duty cycle of two phases of the biased three-phase PWM in the third single closed loop is shown.

[0156] When in use, you can choose to use an independent first single closed loop, a third single closed loop, or a dual closed loop control of the first and third closed loops to control the AC current component and the DC current component, depending on the actual needs, so as to meet a variety of electromagnetic control requirements and ensure the heating effect.

[0157] Compared to the first DC bias mode described above, in the second DC bias mode, the total DC bias current flows through a certain phase lower bridge switch.

[0158] As described above, when using the first and third closed-loop dual-loop control of the AC current component and the DC current component, in order to ensure uniform heating of each phase winding during preheating, the control adjustment module can be configured to execute a combination phase sequence of two adjacent phase PWMs that perform duty cycle adjustment in the second DC bias mode.

[0159] For example, when superimposing DC bias, referring to Figure 11, the rising edges of the high levels of the V-phase PWM and W-phase PWM are first shifted backward by an angle γ11. After a period of time, the rising edges of the high levels of the W-phase PWM and U-phase PWM are shifted backward by an angle γ11. After another period of time, the rising edges of the high levels of the U-phase PWM and V-phase PWM are shifted backward by an angle γ11. This cycle is repeated so that the total DC bias current flows sequentially through the switch T2 of the lower bridge arm of the U-phase, the switch T4 of the lower bridge arm of the V-phase, and the switch T6 of the upper bridge arm of the W-phase, thereby achieving uniform thermal stress on the switches of the inverter unit.

[0160] In some embodiments of this application, when switching to adjust the duty cycle of a two-phase PWM, the phase sequence can be switched by determining whether the heat generation exceeds the set heat generation.

[0161] The heat generation of the three-phase motor windings is calculated during the adjustment of the duty cycles of the U-phase PWM and V-phase PWM.

[0162] When the heat generated by the three-phase motor windings exceeds the set heat generation, the phase sequence of two adjacent phase PWMs in the three-phase PWM is switched to change the phase sequence, and the duty cycle of the V-phase PWM and W-phase PWM is adjusted.

[0163] The heat generation of the three-phase motor windings is calculated during the adjustment of the duty cycle of the V-phase PWM and W-phase PWM signals.

[0164] When the heat generated by the three-phase motor windings exceeds the set heat generation, the phase sequence of two adjacent phase PWMs in the three-phase PWM is switched to change the phase sequence, and the duty cycle of the W-phase PWM and U-phase PWM is adjusted.

[0165] The heat generation of the three-phase motor windings is calculated during the adjustment of the duty cycle of the W-phase PWM and U-phase PWM.

[0166] When the heat generated by the three-phase motor windings exceeds the set heat generation, the phase sequence of two adjacent phase PWMs in the three-phase PWM is switched to change the phase sequence, and the duty cycle of the U-phase PWM and V-phase PWM is adjusted.

[0167] During the adjustment of the duty cycle of two phase PWMs, when the heat generated by the winding exceeds the set heat generated, the combination phase sequence of two adjacent phase PWMs in the three-phase PWM is switched to avoid uneven heating of the three-phase motor windings and ensure the safety of the three-phase motor.

[0168] In some embodiments of this application, the combined phase sequence can also be switched by setting a duration.

[0169] In some embodiments of this application, the original AC current component (see Figure 3) can be configured by a control adjustment module to execute a second DC bias mode to generate a DC bias current and improve the electromagnetic heating effect.

[0170] Referring to Figure 14, the difference between it and Figure 12 is that Figure 14 does not adjust the AC current component and generates DC bias current by executing the second DC bias mode, while Figure 11 superimposes DC bias current on the basis of adjusting the AC current component.

[0171] In some embodiments of this application, referring to Figure 14, taking V-phase PWM and W-phase PWM as examples, as the comparison values ​​of V-phase PWM and W-phase PWM increase to the PWM period setting value (i.e., during the PWM count increment phase), when the PWM comparison value is adjusted to be greater than zero and less than the PWM count setting value, the high-level rising edge output position of V-phase PWM and W-phase PWM is shifted backward by an angle γ greater than zero and less than 60 degrees.

[0172] When the PWM count increases and the PMW comparison value reaches the PWM count setting value, the high-level rising edge of the V-phase PWM and W-phase PWM is shifted backward by an angle γ equal to 60 degrees. During the PWM count decreasing phase (corresponding to the triangular carrier in the S4 interval), when the PMW comparison value is adjusted to be greater than zero and less than the PWM count setting value, the high-level rising edge of the V-phase PWM and W-phase PWM is shifted backward by an angle γ greater than 60 degrees and less than 120 degrees.

[0173] As described above, the electromagnetic heating control system superimposes a DC bias current onto the original AC current component to improve the electromagnetic heating effect. It is suitable for compressors with large winding inductance and resistance and small AC current components.

[0174] In some embodiments of this application, when in use, the electromagnetic heating control system can be selected according to actual needs, including a first single closed loop for controlling the AC current component as described above, a second single closed loop for controlling the DC current component generated using a first DC bias mode, and a third single closed loop for controlling the DC current component generated using a second DC bias mode.

[0175] In this way, a first single closed loop and a switching execution of the second and third single closed loops can be used. The AC current component is adjusted through the first single closed loop, and the phase sequence of the three-phase PWM with duty cycle adjustment in the second single closed loop and the combined phase sequence of the two adjacent phase PWMs with duty cycle adjustment in the third single closed loop are cyclically switched. This achieves the switching of the total DC bias current flowing through the six switching transistors in the inverter unit 20 on the basis of adjusting the AC current component.

[0176] That is, referring to Figure 13, when electromagnetic heating is performed using this electromagnetic heating control system, when the second single closed-loop superimposed DC bias current is used, the total DC bias current circulates through the switch transistor T1 of the upper bridge arm of phase U, the switch transistor T3 of the upper bridge arm of phase V, and the switch transistor T5 of the upper bridge arm of phase W; when the third single closed-loop superimposed DC bias current is used, the total DC bias current circulates through the switch transistor T2 of the lower bridge arm of phase U, the switch transistor T4 of the lower bridge arm of phase V, and the switch transistor T6 of the lower bridge arm of phase W, so that the switch transistors in the inverter unit 20 are heated evenly and the service life of the switch transistors is improved.

[0177] In some embodiments of this application, a DC bias current can also be generated by executing a second DC bias mode based on FIG3. Here, the second DC bias mode is executed by shifting the output position of the V-phase PWM and W-phase PWM high level falling edge forward by γ.

[0178] air conditioner This application also relates to an air conditioner that uses the electromagnetic heating control system described above for preheating, and the compressor starts normally after preheating is completed.

[0179] The air conditioner described above includes a refrigerant circulation loop (not shown), a compressor (not shown), an outdoor heat exchanger (not shown), an indoor heat exchanger (not shown), a four-way valve (not shown), and an electromagnetic heating control system as described above.

[0180] The refrigerant circulation loop allows the refrigerant to circulate in the compressor, condenser, expansion valve, and evaporator.

[0181] In the outdoor heat exchanger and the indoor heat exchanger, one functions as a condenser and the other as an evaporator.

[0182] A four-way valve is used to control the refrigerant flow in the refrigerant circulation loop so that the outdoor heat exchanger and the indoor heat exchanger can switch between condenser and evaporator.

[0183] The compressor is driven by an electric motor and is used to compress low-temperature, low-pressure refrigerant gas into high-temperature, high-pressure refrigerant gas and discharge it to the condenser.

[0184] The AC power generated by the frequency converter topology circuit is used to drive the AC motor of the compressor.

[0185] A preheating time (e.g., time T) can be set, and the period within the preheating time is called the preheating stage.

[0186] When the air conditioner needs to be preheated, the electromagnetic heating control system described above is used to preheat it for the specified time, at which point the preheating stage is complete.

[0187] After the preheating phase is completed, the motor is started using conventional control methods.

[0188] An ambient temperature sensor (not shown) can be installed to detect the ambient temperature of the compressor.

[0189] When the ambient temperature is below the preset temperature threshold, the outdoor unit of the air conditioner is considered to be in a low ambient temperature condition.

[0190] Under low ambient temperature conditions, the compressor needs to be preheated before starting to ensure reliable startup; otherwise, compressor preheating is not required.

[0191] Thus, at low ambient temperatures, the compressor is preheated by the electromagnetic heating control system, which can regulate the current component by controlling the DC current component and / or the AC current component, thereby ensuring the efficiency of electromagnetic heating.

[0192] Furthermore, it can set different DC current component commands and / or AC current components based on different ambient temperatures and different motors, and reasonably set the preheating time, thus adapting to different degrees of motor body preheating, and is highly flexible in use.

[0193] Furthermore, this electromagnetic heating control scheme is simple and reliable, and is suitable for applications such as air conditioners.

[0194] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0195] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An electromagnetic heating control system, characterized in that, include: The variable frequency topology circuit structure includes an inverter unit, a triangular carrier wave and a PWM comparison value are compared and output to control the three-phase PWM of the switching transistors in the inverter unit, the phase angle corresponding to the PWM count of the triangular carrier wave between zero and the PWM period set value is 60 degrees; a control adjustment module is configured to, when heating of the AC motor driven by the inverter unit is required, adjust the duty cycle of two phase PWMs to be different from the duty cycle of the remaining phase PWM, such that the phase difference between the two phase PWMs is 120 degrees, the phase difference between one phase PWM and the remaining phase PWM is greater than 120 degrees, and the phase difference between the other phase PWM and the remaining phase PWM is less than 120 degrees; wherein, before adjustment, the period of each phase PWM is three times the PWM period.

2. The electromagnetic heating control system according to claim 1, characterized in that, The control adjustment module adjusts the duty cycle of two of the PWM phases to be different from the duty cycle of the remaining PWM phase. Specifically, for the triangular carrier corresponding to the high level of each of the three PWM phases, the comparison value of two of the PWM phases is adjusted from zero to a non-zero value, so that the output position of the high level rising edge of the two PWM phases is shifted backward by angle α1 or forward by angle α2, or the output position of the high level falling edge of the two PWM phases is shifted forward by angle α3 or backward by angle α4.

3. The electromagnetic heating control system according to claim 2, characterized in that, The control adjustment module is further configured to: acquire the actual DC current component; increase or decrease the offset angle according to the instruction value corresponding to the DC current component instruction and the actual DC current component, so that the actual DC current component is equal to the DC current component.

4. The electromagnetic heating control system according to claim 2, characterized in that, Specifically, the high-level rising edge output positions of two phases of the PWM are offset backward by an angle α1. Specifically: during the PWM count increment phase, when the PMW comparison value is adjusted to be greater than zero and less than the PWM count setting value, the high-level rising edge output positions of the two phases of the PWM are offset backward by an angle α1 greater than zero and less than 60 degrees; when the PWM count increments and the PMW comparison value reaches the PWM count setting value, the high-level rising edge output positions of the two phases of the PWM are offset backward by an angle α1 equal to 60 degrees; during the PWM count decrement phase, when the PMW comparison value is adjusted to be greater than zero and less than the PWM count setting value, the high-level rising edge output positions of the two phases of the PWM are offset backward by an angle α1 greater than 60 degrees and less than 120 degrees.

5. The electromagnetic heating control system according to claim 1, characterized in that, The control adjustment module is also configured to: cyclically switch the combined phase sequence of two adjacent phases in a three-phase PWM for duty cycle adjustment.

6. The electromagnetic heating control system according to claim 5, characterized in that, The control adjustment module switches the phase sequence by determining whether the heat generated by the three-phase motor windings exceeds the set heat generated.

7. The electromagnetic heating control system according to claim 6, characterized in that, The phase sequence is switched by determining whether the heat generation of the three-phase motor windings exceeds a set heat generation value. Specifically: S1: During the duty cycle adjustment of the two-phase PWM corresponding to the first phase sequence, the heat generation of the three-phase motor windings is calculated; S2: When the heat generation of the three-phase motor windings exceeds the set heat generation value, the first phase sequence is switched to the second phase sequence; S3: During the duty cycle adjustment of the two-phase PWM corresponding to the second phase sequence, the heat generation of the three-phase motor windings is calculated; S4: When the heat generation of the three-phase motor windings exceeds the set heat generation value, the second phase sequence is switched to the third phase sequence; S5: During the duty cycle adjustment of the two-phase PWM corresponding to the third phase sequence, the heat generation of the three-phase motor windings is calculated; S6: When the heat generation of the three-phase motor windings exceeds the set heat generation value, the third phase sequence is switched back to the first phase sequence, and the process returns to S1.

8. An electromagnetic heating control system, characterized in that, include: The variable frequency topology circuit structure includes an inverter unit, a triangular carrier wave and a PWM comparison value are compared and output to control the three-phase PWM of the switching transistors in the inverter unit, the phase angle corresponding to the PWM count of the triangular carrier wave between zero and the PWM period set value is 60 degrees; a control adjustment module is configured to execute a first DC bias mode and a second DC bias mode when heating of the AC motor driven by the inverter unit is required; in the first DC bias mode, the duty cycle of a certain phase PWM is adjusted to be different from the duty cycles of the remaining two phase PWMs, such that the phase difference between the remaining two phase PWMs is 120 degrees, and the phase difference between one phase PWM and the first phase PWM is greater than 120 degrees, while the other phase PWM of the remaining two phase PWMs is greater than 120 degrees. The phase difference between the PWM and a certain phase PWM is less than 120 degrees; in the second DC bias mode, the duty cycle of two of the PWMs is adjusted to be different from the duty cycle of the remaining PWM, so that the phase difference between the two of the PWMs is 120 degrees, the phase difference between one of the two PWMs and the remaining PWM is greater than 120 degrees, and the phase difference between the other of the two PWMs and the remaining PWM is less than 120 degrees; the control adjustment module is further configured to: cyclically switch the phase sequence of the three-phase PWMs with duty cycle adjustment in the first DC bias mode and the combined phase sequence of the two-phase PWMs with duty cycle adjustment in the second DC bias mode; wherein, before adjustment, the period of each phase PWM is three times the PWM period.

9. An air conditioner, characterized in that, include: The refrigerant circulation loop circulates the refrigerant through the compressor, condenser, expansion valve, and evaporator. The compressor, driven by a motor, compresses the low-temperature, low-pressure refrigerant gas into a high-temperature, high-pressure refrigerant gas and discharges it to the condenser. The variable frequency topology circuit includes an inverter unit. A triangular carrier wave is compared with a PWM comparison value, and a three-phase PWM is output to control the switching transistors in the inverter unit. The phase angle corresponding to the PWM count of the triangular carrier wave between zero and the PWM period set value is 60 degrees. A control adjustment module is configured to, when heating the AC motor driven by the inverter unit is required, adjust the duty cycle of two phase PWMs to be different from the duty cycle of the remaining phase PWM, such that the phase difference between the two phase PWMs is 120 degrees, the phase difference between one phase PWM and the remaining phase PWM is greater than 120 degrees, and the phase difference between the other phase PWM and the remaining phase PWM is less than 120 degrees. Before adjustment, the period of each phase PWM is three times the PWM period.

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