CN109494973B - PFC control method and device, PFC circuit and motor drive circuit - Google Patents

PFC control method and device, PFC circuit and motor drive circuit Download PDF

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CN109494973B
CN109494973B CN201811574920.9A CN201811574920A CN109494973B CN 109494973 B CN109494973 B CN 109494973B CN 201811574920 A CN201811574920 A CN 201811574920A CN 109494973 B CN109494973 B CN 109494973B
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input
pfc circuit
pfc
bus
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CN109494973A (en
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王甫敬
盛爽
夏瑞
郑长春
黄勇
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Guangdong Xita Frequency Conversion Technology Co ltd
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Guangdong Xita Frequency Conversion Technology Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
    • H02M1/4208—Arrangements for improving power factor of AC input
    • H02M1/4225—Arrangements for improving power factor of AC input using a non-isolated boost converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
    • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
    • H02P27/085—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation wherein the PWM mode is adapted on the running conditions of the motor, e.g. the switching frequency
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Power Engineering (AREA)
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Abstract

The invention relates to the field of PFC control, and discloses a PFC circuit control method, a PFC circuit control device, a PFC circuit control circuit and a motor drive circuit. The boost ratio coefficient calculated according to the voltage average value can timely follow the change of the bus voltage and the input current, the reasonable setting of the boost ratio coefficient under the ultra-low voltage environment is guaranteed, and finally the switching tube of the PFC circuit is controlled to work according to the duty ratio determined by the boost ratio coefficient to obtain a reasonable bus voltage, so that the motor driving circuit is in a proper state, and the safety of devices in the circuit is guaranteed against damage.

Description

PFC control method and device, PFC circuit and motor drive circuit
Technical Field
The invention relates to the field of PFC control, in particular to a PFC circuit control method and device, a PFC circuit and a motor drive circuit.
Background
The Power Factor Correction (PFC) circuit is widely applied to current frequency-variable home appliances such as frequency-variable air conditioners, refrigerators, washing machines, and other home appliances, and when designing a PFC circuit, the range of the dc bus voltage and the range of the boost ratio coefficient of the PFC controller are generally designed only for the range of the Power supply voltage of 160V to 220V. In a regional power grid, particularly a rural power grid, the load capacity of a power grid is poor, the voltage drops severely when the load is large, for example, the power supply voltage of the power grid is lowered to about 140V seriously in a time period when the air conditioner is used more in summer, so that the PFC circuit cannot work at this time, and the frequency conversion household appliance is shut down due to insufficient voltage.
Disclosure of Invention
The invention aims to provide a PFC circuit control method, a PFC circuit control device, a PFC circuit and a motor driving circuit, and aims to solve the problem that the existing PFC circuit cannot adapt to an ultra-low voltage environment, so that a corresponding variable-frequency household appliance cannot work in the voltage environment and is stopped.
In order to achieve the above object, the present invention provides a PFC circuit control method, the PFC circuit being applied to a motor drive circuit including a rectifier circuit, a controller, and an inverter, the control method comprising:
acquiring input current of a PFC circuit, and determining input average current of the PFC circuit according to the input current;
acquiring bus current output by the PFC circuit, acquiring bus voltage output by the PFC circuit, and determining an input voltage average value of the PFC circuit according to the bus voltage, the bus current and the input average current;
determining a boost ratio coefficient according to the bus voltage and the average value of the input voltage;
determining the duty ratio of a switching tube for driving the PFC circuit according to the boost ratio coefficient, the input average current and the input current;
and controlling the switching tube to perform switching action according to the duty ratio so as to control the PFC circuit to work.
Alternatively, the boost ratio coefficient ranges from π/2 to π.
Optionally, the control method further includes:
determining a filtering value of the bus current according to the bus current;
and determining the average value of the input voltage of the PFC circuit according to the bus voltage, the filtered value of the bus current and the input average current.
Optionally, determining the input average current of the PFC circuit from the input current comprises:
under the condition that the current PFC control period is in the last PFC control period in the current period of the input current, calculating the average current in the current input current period;
and under the condition that the current PFC control period is not in the last PFC control period in the current period of the input current, acquiring the average current of the previous period of the input current.
In order to achieve the above object, the present invention also provides a PFC circuit control apparatus, a motor drive circuit including a rectifier circuit, a controller, and an inverter, characterized in that the PFC circuit control apparatus includes:
the input current sampling module is used for collecting the input current of the PFC circuit;
the voltage sampling module is used for collecting bus voltage output by the PFC circuit;
the output current sampling module is used for collecting the output current of the PFC circuit;
the controller is configured to: the method comprises the steps of obtaining input current of a PFC circuit from an input current sampling module, determining input average current of the PFC circuit according to the input current, obtaining output current of the PFC circuit from an output current sampling module, obtaining bus voltage output by the PFC circuit from a voltage sampling module, determining input voltage average value of the PFC circuit according to the bus voltage, the bus current and the input average current, determining a boost ratio coefficient according to the bus voltage and the input voltage average value, determining duty ratio of a switching tube for driving the PFC circuit according to the boost ratio coefficient, the input average current and the input current, and controlling the switching tube to perform switching action according to the duty ratio to control the PFC circuit to work.
Alternatively, the boost ratio coefficient ranges from π/2 to π.
Optionally, the controller is further configured to:
determining a filtering value of the bus current according to the bus current;
and determining the average value of the input voltage of the PFC circuit according to the bus voltage, the filtered value of the bus current and the input average current.
Optionally, the controller being configured to determine the input average current of the PFC circuit from the input current comprises:
under the condition that the current PFC control period is in the last PFC control period in the current period of the input current, calculating the average current in the current input current period;
and under the condition that the current PFC control period is not in the last PFC control period in the current period of the input current, acquiring the average current of the previous period of the input current.
In order to achieve the above object, the present invention further provides a PFC circuit including an inductor, a switching tube and a fast recovery diode, characterized in that the PFC circuit further includes a PFC circuit control apparatus according to any one of claims 5 to 8;
one end of the inductor is the positive electrode of the input end of the PFC circuit, the other end of the inductor is connected with the input end of the switch tube and the positive electrode of the fast recovery diode in a common mode, the cathode of the fast recovery diode is the positive electrode of the output end of the PFC circuit, the output end of the switch tube is connected with the negative electrode of the output end of the PFC circuit, and the control end of the switch tube is the control end of the PFC circuit.
Through the technical scheme, the invention also provides a motor driving circuit, which comprises a rectifying module and a filtering module and is characterized by also comprising the PFC circuit of claim 9;
the output end of the rectification module is connected with the input end of the PFC circuit, and the rectification module is used for rectifying alternating current input into the motor driving circuit and outputting pulsating direct current;
the filtering module is connected with the output end of the PFC circuit and used for filtering the direct current output by the PFC circuit and outputting smooth direct current, and the filtering module is connected with the direct current bus and supplies power to the motor driving circuit through the direct current bus.
According to the technical scheme, the method for controlling the PFC circuit comprises the steps of obtaining input current of the PFC circuit, determining input average current of the PFC circuit according to the input current, obtaining bus current output by the PFC circuit, obtaining bus voltage output by the PFC circuit, determining an input voltage average value of the PFC circuit according to the bus voltage, the bus current and the input average current, determining a boost ratio coefficient according to the bus voltage and the input voltage average value, determining a duty ratio D of a switching tube for driving the PFC circuit according to the boost ratio coefficient, the input average current and the input current, and finally controlling the switching tube to perform switching action according to the duty ratio D to control the PFC circuit to work. Because the average value of the input voltage is related to the bus voltage at the output side of the PFC circuit, the bus current and the input average current at the input side of the PFC circuit when being calculated, the boost ratio coefficient calculated according to the average value of the voltage can timely follow the change of the bus voltage and the input current, the reasonable setting of the boost ratio coefficient under the ultra-low voltage environment can be ensured, and finally the switch tube of the PFC circuit is controlled to work according to the duty ratio determined by the boost ratio coefficient to obtain a reasonable bus voltage. Therefore, the motor driving circuit is in a proper state, and the safety of devices in the circuit is ensured without being damaged.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
fig. 1 is a circuit schematic diagram of a motor drive circuit of a PFC circuit control method according to an embodiment of the present invention;
fig. 2 is a flowchart of a PFC circuit control method according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of waveforms of input current, control period and average current;
FIG. 4 is a waveform diagram of input current, input current magnitude, and input average current;
fig. 5 is a schematic diagram of the relationship between the duty ratio and the boosting ratio coefficient.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
It should be noted that, if directional indications (such as up, down, left, right, front, and back … …) are involved in the embodiment of the present invention, the directional indications are only used to explain the relative positional relationship between the components, the movement situation, and the like in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indications are changed accordingly.
In addition, if there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.
The embodiment of the present invention provides a method for controlling a PFC circuit, where the PFC circuit is used for a motor driving circuit, the motor is a permanent magnet synchronous motor, and as shown in a simplified circuit diagram of the motor driving circuit in fig. 1, the motor driving circuit includes a rectifying module 60, a PFC module 50, a filtering module 70, a controller 10, an inverter 80, a voltage sampling module 30, an input current sampling module 20, and an output current sampling module 40, where the rectifying module 60 rectifies input ac into pulsating dc, and the circuit may be a bridge rectifier circuit in the drawing; the PFC module 50 is configured to perform power factor correction on the pulsating direct current output by the rectifier module 60, the filter module 70 filters the direct current output by the PFC module 50 to convert the direct current into smooth direct current, and the filter module 70 is mainly composed of a large-capacity electrolytic capacitor (for example, 400uF/450V) and supplies power to the inverter 80 by connecting a direct current bus; the voltage sampling module 30 is configured to collect the dc bus voltage Vdc and output the dc bus voltage Vdc to the controller 10, the input current sampling module 20 is mainly composed of a single resistor R1, and is connected in series to a power line of the rectifier module 60 and the PFC module 50, and is configured to collect the input current Ibd output from the rectifier module 60 and entering the PFC module 50, the output current sampling module 40 is connected in series and mainly composed of a single resistor R2, and is connected in series to the dc bus return, and is configured to collect the bus current Idc, and the controller 10 is configured to generate a PWM signal for controlling the operation of the switching tube IGBT of the PFC module 50, so as to control the operation of the PFC module 50; meanwhile, the controller 10 generates three-phase currents of three-phase windings of the driving motor 90 of the inverter 80 by calculation according to the bus current Idc, and the controller 10 performs vector control according to the direct-current bus voltage Vdc and the three-phase currents, and finally generates PWM signals for driving six switching tubes of the inverter 80 so as to control the inverter 80 to drive the driving motor 90 to operate.
As shown in fig. 2, the single-resistor sampling-based controllable method based on the motor driving circuit includes:
step S210, acquiring an input current Ibd of the PFC circuit, and determining an input average current Ibd _ ave of the PFC circuit according to the input current Ibd;
step S220, obtaining a bus current Idc output by the PFC circuit, obtaining a bus voltage Vdc output by the PFC circuit, and determining an input voltage average value Vbd _ ave of the PFC circuit according to the bus voltage Vdc, the bus current Idc and the input average current Ibd _ ave;
step S230, obtaining a bus voltage given value Vdc _ ref, and determining a boost ratio coefficient Ka according to the bus voltage given value Vdc _ ref and an input voltage average value Vbd _ ave;
step 240, determining a duty ratio D of a switching tube for driving the PFC circuit according to the boost ratio coefficient Ka, the input average current Ibd _ ave and the input current Ibd;
and S250, controlling the switching tube to perform switching action according to the duty ratio D so as to control the PFC circuit to work.
In step S210, an input current Ibd is collected by the input current sampling module 20, where the current is an output current of the bridge rectifier 60, and taking the kth PWM control period of the IGBT as an example, the average current Ibd _ ave in one input current period T is:
Figure GDA0001955327870000071
wherein Ts is a PWM control period, a unit calculation step size, T is a period of the input current Ibd, N is the number of input current periods, and a waveform diagram of the input current Ibd, the control period Ts, and the average current Ibd _ ave is shown in fig. 3, where the input current Ibd is a current output by the rectifier module 60, as can be seen from fig. 3, the period is a half of an external input ac period, for example, 220V/50Hz ac is taken as an example, and T is 10ms at this time. Combining the above formula, it can be known that, the average current Ibd _ ave is updated once for each input current period T, taking the current cycle as the nth input current period as an example, if the current control period Ts is the last calculation step in the current cycle of the input current Ibd, the average current Ibd _ ave (N) in the current cycle can be directly calculated, otherwise, the average current Ibd _ ave (N-1) in the previous input current cycle is used, and the average current Ibd _ ave in the nth cycle is calculated according to the following formula:
Figure GDA0001955327870000072
wherein n is T/Ts
In step S220, the bus current Idc is obtained through the output current sampling module 40, the dc bus voltage Vdc is obtained through the voltage sampling module 30, and the average value Vbd _ ave of the input voltage is calculated according to the principle that the input power and the output power of the PFC circuit are approximately equal, where the specific formula is as follows:
Figure GDA0001955327870000073
where K is the current PWM control cycle number.
Furthermore, the first-order filtering can be performed on the bus current Idc to obtain a filtered value Idc _ fil of the bus current Idc, so that the condition that the collected value is inaccurate due to the fact that interference signals affect the collected bus current Idc is avoided, and the calculation formula is as follows:
Idc_fil(k)＝(ωcTs)Idc(k-1)+(1-ωcTs)Idc_fil(k-1)
wherein ω iscFor the cutoff frequency parameter, Ts is the PWM control period.
And calculating the average value Vbd _ ave of the input voltage in the formula by adopting the filtered value Idc _ fil of the bus current Idc instead of the bus current Idc, so that the value calculation accurately avoids the fluctuation of a calculation result caused by an interference signal.
In step S230, the bus voltage given value Vdc _ ref is a set bus voltage value, and when the motor driving circuit operates in a low power voltage environment, the bus voltage given value Vdc _ ref needs to be between Vdc _ min and Vdc _ max, such as when the effective value of the externally input ac voltage is 220V, Vdc _ min is 200V and Vdc _ max is 400V. Further, for household appliances such as air conditioners, refrigerators and the like, the rated value of the voltage of the motor is 200-220V, and assuming that the frequency conversion controller always operates in the linear modulation region, for the 220V motor, the bus voltage to be loaded on the inverter 80 side is as follows:
Figure GDA0001955327870000081
therefore, for an input voltage of 220V, the given value Vdc _ ref of the bus voltage can be set to 311V, wherein Vac _ rms is an effective value of the alternating voltage.
Determining a boost ratio coefficient Ka of the current PWM control period k according to the bus voltage Vdc and the input voltage average value Vbd _ ave according to the following formula:
Figure GDA0001955327870000082
in step S240, determining the duty ratio D of the switching tube driving the PFC circuit according to the boost ratio coefficient Ka, the input average current Ibd _ ave, and the input current Ibd according to the existing PFC single-cycle algorithm calculation formula:
Figure GDA0001955327870000083
finally, the PFC control unit 11 outputs a corresponding PWM control signal according to the duty ratio to control the operation of the switching tube IGBT, thereby implementing the control of power factor correction for the PFC circuit.
The method for controlling the PFC circuit of the embodiment of the invention comprises the steps of obtaining input current of the PFC circuit, determining input average current of the PFC circuit according to the input current, obtaining bus current output by the PFC circuit, obtaining bus voltage output by the PFC circuit, determining input voltage average value of the PFC circuit according to the bus voltage, the bus current and the input average current, determining a boost ratio coefficient according to the bus voltage and the input voltage average value, determining a duty ratio D of a switching tube for driving the PFC circuit according to the boost ratio coefficient, the input average current and the input current, and finally controlling the switching tube to perform switching action according to the duty ratio D to control the PFC circuit to work. Because the average value of the input voltage is related to the bus voltage at the output side of the PFC circuit, the bus current and the input average current at the input side of the PFC circuit when being calculated, the boost ratio coefficient calculated according to the average value of the voltage can timely follow the change of the bus voltage and the input current, the reasonable setting of the boost ratio coefficient under the ultra-low voltage environment can be ensured, and finally the switch tube of the PFC circuit is controlled to work according to the duty ratio determined by the boost ratio coefficient to obtain a reasonable bus voltage. Therefore, the motor driving circuit is in a proper state, and the safety of devices in the circuit is ensured without being damaged.
Further, after the step-up ratio coefficient ka (k) is obtained by the above calculation, the range is further limited and corrected.
According to the calculation formula of the duty ratio D:
Figure GDA0001955327870000091
the calculation formula of the input current Ibd and the input current amplitude Ibd _ mag is as follows:
Ibd＝Ibd_mag|sinθ|，
the average value Ibd _ ave over a period of the input current is:
Figure GDA0001955327870000092
the waveform relationship among the Ibd, the Ibd _ mag, and the Ibd _ ave is shown in fig. 4, and the duty ratio D calculation formula is substituted with the calculation formulas of the Ibd and the Ibd _ ave to obtain:
Figure GDA0001955327870000101
the relationship between the duty ratio D and the voltage boosting ratio coefficient Ka is shown in fig. 5, and it can be known from fig. 5 that when Ka < pi/2, the duty ratio D is smaller than 0, which is not allowed in practical control, so D is limited to 0, and at this time, a non-conducting area of the switching tube IGBT occurs, which means that the alternating current side current is not controllable, which causes a current distortion spike, and meanwhile, the power factor is far smaller than 1, so Ka needs to be larger than or equal to pi/2.
When Ka is greater than pi, the duty ratio D curves are all over 0.5 numerical value, namely the turn-on time of the IGBT of the PFC power switch device is always greater than the turn-off time, at the moment, the current harmonic wave on the alternating current side is large, in addition, the turn-on time of the IGBT device is long, the heating is serious, and therefore Ka needs to be less than pi.
Therefore, the value range of the voltage boosting ratio coefficient Ka is pi/2-pi.
Further, when the voltage boosting ratio coefficient Ka exceeds the value range pi/2-pi, i.e., 1.57-3.14, the bus voltage given value Vdc _ ref needs to be corrected according to the limited voltage boosting ratio coefficient Ka, so that the finally calculated voltage boosting ratio coefficient Ka is within the range.
For example, in the case of each medium voltage effective value input from the outside, if the bus voltage given value Vdc _ ref is 350V, each boost ratio coefficient and the actual bus voltage given value Vdc _ ref obtained in practice are as follows:
Figure GDA0001955327870000102
Figure GDA0001955327870000111
the calculated value of the voltage boosting ratio coefficient Ka in the second row, the actually set value of the voltage boosting ratio coefficient Ka in the third row, and the actually set value Vdc _ ref in the fourth row, it can be seen that when the external voltage in the first row is higher, the calculated value of the voltage boosting ratio coefficient Ka already exceeds the lowest value, i.e. 1.57, of the above-mentioned value range, and therefore the value is forcibly limited to the minimum value of 1.57, so that the corresponding set value Vdc _ ref of the bus voltage needs to be adjusted higher, and the finally calculated voltage boosting ratio coefficient Ka meets the above-mentioned range requirement. Similarly, in the third row to the first row from the last, the calculated value of the step-up ratio coefficient Ka already exceeds the highest value of the above-mentioned value range, i.e. 3.14, and is therefore constrained to be the highest value of 3.14, so that the corresponding bus voltage set value Vdc _ ref needs to be adjusted down, so that the finally calculated step-up ratio coefficient Ka meets the above-mentioned range requirement.
The embodiment of the present invention also provides a PFC circuit control apparatus, which is used for a motor driving circuit, such as the motor driving circuit simplified circuit diagram shown in fig. 1, the motor driving circuit includes a rectifying module 60, a PFC module 50, a filtering module 70, a controller 10 and an inverter 80, wherein the rectifying module 60 rectifies input alternating current into pulsating direct current, and the circuit may be a bridge rectifier circuit in the figure; the PFC module 50 is configured to perform power factor correction on the pulsating direct current output by the rectifier module 60, the filter module 70 filters the direct current output by the PFC module 50 to convert the direct current into smooth direct current, and the filter module 70 is mainly composed of a large-capacity electrolytic capacitor (for example, 400uF/450V) and supplies power to the inverter 80 by connecting a direct current bus. The PFC circuit control device includes:
an input current sampling module 20, configured to collect an input current of the PFC circuit;
the voltage sampling module 30 is used for collecting bus voltage output by the PFC circuit;
the output current sampling module 40 is used for collecting the output current of the PFC circuit;
the controller 10 is configured to: the method comprises the steps of obtaining input current of a PFC circuit from an input current sampling module 20, determining input average current of the PFC circuit according to the input current, obtaining output current of the PFC circuit from an output current sampling module 40, obtaining bus voltage output by the PFC circuit from a voltage sampling module 30, determining an input voltage average value of the PFC circuit according to the bus voltage, a filter value of the bus current and the input average current, determining a boost ratio coefficient according to the bus voltage and the input voltage average value, determining a duty ratio of a switching tube for driving the PFC circuit according to the boost ratio coefficient, the input average current and the input current, and controlling the switching tube to perform switching action according to the duty ratio to control the PFC circuit to work.
The input current Ibd is collected by the input current sampling module 20, and the current is the output current of the bridge rectifier 60, where taking the kth PWM control period of the IGBT as an example, the average current Ibd _ ave in one input current period T is:
Figure GDA0001955327870000121
wherein Ts is a PWM control period, a unit calculation step size, T is a period of the input current Ibd, N is the number of input current periods, and a waveform diagram of the input current Ibd, the control period Ts, and the average current Ibd _ ave is shown in fig. 3, where the input current Ibd is a current output by the rectifier module 60, as can be seen from fig. 3, the period is a half of an external input ac period, for example, 220V/50Hz ac is taken as an example, and T is 10ms at this time. Combining the above formula, it can be known that, the average current Ibd _ ave is updated once for each input current period T, taking the current cycle as the nth input current period as an example, if the current control period Ts is the last calculation step in the current cycle of the input current Ibd, the average current Ibd _ ave (N) in the current cycle can be directly calculated, otherwise, the average current Ibd _ ave (N-1) in the previous input current cycle is used, and the average current Ibd _ ave in the nth cycle is calculated according to the following formula:
Figure GDA0001955327870000131
wherein n is T/Ts
Then, the bus current Idc is obtained through the output current sampling module 40, the dc bus voltage Vdc is obtained through the voltage sampling module 30, and the average value Vbd _ ave of the input voltage is calculated according to the principle that the input power and the output power of the PFC circuit are approximately equal, wherein the specific formula is as follows:
Figure GDA0001955327870000132
where K is the current PWM control cycle number.
Furthermore, the first-order filtering can be performed on the bus current Idc to obtain a filtered value Idc _ fil of the bus current Idc, so that the condition that the collected value is inaccurate due to the fact that interference signals affect the collected bus current Idc is avoided, and the calculation formula is as follows:
Idc_fil(k)＝(ωcTs)Idc(k-1)+(1-ωcTs)Idc_fil(k-1)
wherein ω iscFor the cutoff frequency parameter, Ts is the PWM control period.
And calculating the average value Vbd _ ave of the input voltage in the formula by adopting the filtered value Idc _ fil of the bus current Idc instead of the bus current Idc, so that the value calculation accurately avoids the fluctuation of a calculation result caused by an interference signal.
The bus voltage given value Vdc _ ref is a set bus voltage value, and when the motor driving circuit operates in a low power voltage environment, the bus voltage given value Vdc _ ref needs to be between Vdc _ min and Vdc _ max, for example, when the effective value of the externally input alternating voltage is 220V, Vdc _ min is 200V, and Vdc _ max is 400V. Further, for household appliances such as air conditioners, refrigerators and the like, the rated value of the voltage of the motor is 200-220V, and assuming that the frequency conversion controller always operates in the linear modulation region, for the 220V motor, the bus voltage to be loaded on the inverter 80 side is as follows:
Figure GDA0001955327870000141
therefore, for an input voltage of 220V, the given value Vdc _ ref of the bus voltage can be set to 311V, wherein Vac _ rms is an effective value of the alternating voltage.
Determining a boost ratio coefficient Ka of the current PWM control period k according to the bus voltage Vdc and the input voltage average value Vbd _ ave according to the following formula:
Figure GDA0001955327870000142
determining the duty ratio D of a switching tube for driving the PFC circuit according to the boosting ratio coefficient Ka, the input average current Ibd _ ave and the input current Ibd, and calculating according to the existing PFC single-cycle algorithm:
Figure GDA0001955327870000143
finally, the PFC control unit 11 outputs a corresponding PWM control signal according to the duty ratio to control the operation of the switching tube IGBT, thereby implementing the control of power factor correction for the PFC circuit.
The PFC circuit control apparatus of the embodiment of the present invention obtains an input current of a PFC circuit through an input current sampling module 20, determines an input average current of the PFC circuit according to the input current, obtains a bus current output by the PFC circuit through an output current sampling module 40, obtains a bus voltage output by the PFC circuit through a voltage sampling module 30, determines an input voltage average value of the PFC circuit according to the bus voltage, the bus current, and the input average current, determines a step-up ratio coefficient according to the bus voltage and the input voltage average value, determines a duty ratio D of a switching tube driving the PFC circuit according to the step-up ratio coefficient, the input average current, and the input current, and finally controls the switching tube to perform a switching operation according to the duty ratio D to control the PFC circuit to operate. Because the average value of the input voltage is related to the bus voltage at the output side of the PFC circuit, the bus current and the input average current at the input side of the PFC circuit when being calculated, the boost ratio coefficient calculated according to the average value of the voltage can timely follow the change of the bus voltage and the input current, the reasonable setting of the boost ratio coefficient under the ultra-low voltage environment can be ensured, and finally the switch tube of the PFC circuit is controlled to work according to the duty ratio determined by the boost ratio coefficient to obtain a reasonable bus voltage. Therefore, the motor driving circuit is in a proper state, and the safety of devices in the circuit is ensured without being damaged.
Further, after the step-up ratio coefficient ka (k) is obtained by the above calculation, the range is further limited and corrected.
According to the calculation formula of the duty ratio D:
Figure GDA0001955327870000151
the calculation formula of the input current Ibd and the input current amplitude Ibd _ mag is as follows:
Ibd＝Ibd_mag|sinθ|，
the average value Ibd _ ave over a period of the input current is:
Figure GDA0001955327870000152
the waveform relationship among the Ibd, the Ibd _ mag, and the Ibd _ ave is shown in fig. 4, and the duty ratio D calculation formula is substituted with the calculation formulas of the Ibd and the Ibd _ ave to obtain:
Figure GDA0001955327870000153
the relationship between the duty ratio D and the voltage boosting ratio coefficient Ka is shown in fig. 5, and it can be known from fig. 5 that when Ka < pi/2, the duty ratio D is smaller than 0, which is not allowed in practical control, so D is limited to 0, and at this time, a non-conducting area of the switching tube IGBT occurs, which means that the alternating current side current is not controllable, which causes a current distortion spike, and meanwhile, the power factor is far smaller than 1, so Ka needs to be larger than or equal to pi/2.
When Ka is greater than pi, the duty ratio D curves are all over 0.5 numerical value, namely the turn-on time of the IGBT of the PFC power switch device is always greater than the turn-off time, at the moment, the current harmonic wave on the alternating current side is large, in addition, the turn-on time of the IGBT device is long, the heating is serious, and therefore Ka needs to be less than pi.
Therefore, the value range of the voltage boosting ratio coefficient Ka is pi/2-pi.
Further, when the voltage boosting ratio coefficient Ka exceeds the value range pi/2-pi, i.e., 1.57-3.14, the bus voltage given value Vdc _ ref needs to be corrected according to the limited voltage boosting ratio coefficient Ka, so that the finally calculated voltage boosting ratio coefficient Ka is within the range.
For example, in the case of each medium voltage effective value input from the outside, if the bus voltage given value Vdc _ ref is 350V, each boost ratio coefficient and the actual bus voltage given value Vdc _ ref obtained in practice are as follows:
Figure GDA0001955327870000161
the calculated value of the voltage boosting ratio coefficient Ka in the second row, the actually set value of the voltage boosting ratio coefficient Ka in the third row, and the actually set value Vdc _ ref in the fourth row, it can be seen that when the external voltage in the first row is higher, the calculated value of the voltage boosting ratio coefficient Ka already exceeds the lowest value, i.e. 1.57, of the above-mentioned value range, and therefore the value is forcibly limited to the minimum value of 1.57, so that the corresponding set value Vdc _ ref of the bus voltage needs to be adjusted higher, and the finally calculated voltage boosting ratio coefficient Ka meets the above-mentioned range requirement. Similarly, in the third row to the first row from the last, the calculated value of the step-up ratio coefficient Ka already exceeds the highest value of the above-mentioned value range, i.e. 3.14, and is therefore constrained to be the highest value of 3.14, so that the corresponding bus voltage set value Vdc _ ref needs to be adjusted down, so that the finally calculated step-up ratio coefficient Ka meets the above-mentioned range requirement.
The embodiment of the invention also provides a PFC circuit and a motor driving circuit applied to the PFC circuit, as shown in fig. 1, the PFC circuit comprises an inductor L, a switching tube IGBT and a fast recovery diode FRD, and further comprises the PFC circuit control device. In fig. 1, one end of the inductor L is the positive electrode of the input end of the PFC circuit, the other end of the inductor L is connected to the input end, i.e., the C electrode, of the switching tube IGBT and the positive electrode of the fast recovery diode FRD, the cathode of the fast recovery diode FRD is the output end of the PFC circuit, the output end, i.e., the E electrode, of the switching tube IGBT is connected to the input and output ends of the PFC current, and the control end, i.e., the G electrode, of the switching tube IGBT is the control end of the PFC. The motor driving circuit comprises a rectifying module 60, a filtering module 70, an inverter 80 and the PFC circuit, and can be applied to household appliances working through loads such as a permanent magnet synchronous motor, a variable frequency compressor and the like, such as a variable frequency air conditioner, a variable frequency refrigerator or a variable frequency washing machine.
The PFC circuit realizes safe work in a low-voltage environment, outputs reasonable bus voltage to supply power for the subsequent inverter 80, enables the inverter 80 to still drive the motor 90 to work in the low-voltage environment, enables the motor 90 to be in a proper working state, and still can effectively output capacity, and enables household appliances such as air conditioners applying the motor driving circuit to still output effective refrigerating/heating capacity in the low-voltage environment.
Embodiments of the present invention also provide a computer program product comprising program instructions that, when executed by a controller, enable the controller to implement any of the above-described motor drive control methods for single resistance sampling.
Embodiments of the present invention also provide a storage medium having computer readable instructions stored thereon, which when executed by a controller, enable the controller to perform any of the above-described motor drive control methods for single resistance sampling.
Those skilled in the art can understand that all or part of the steps in the method for implementing the above embodiments may be implemented by a program to instruct related hardware, where the program is stored in a storage medium and includes several instructions to enable a (may be a single chip, a chip, etc.) or a processor (processor) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
In the description herein, references to the description of the terms "first embodiment," "second embodiment," "example," etc., mean that a particular method, apparatus, or feature described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, methods, apparatuses, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims (8)

1. A control method for a power factor correction PFC circuit applied to a motor drive circuit including a rectifier circuit, a controller, and an inverter, the control method comprising:
acquiring the input current of the PFC circuit, and determining the input average current of the PFC circuit according to the input current;
acquiring bus current output by the PFC circuit, acquiring bus voltage output by the PFC circuit, and determining an input voltage average value of the PFC circuit according to the bus voltage, the bus current and the input average current;
determining a boost ratio coefficient according to the given value of the bus voltage and the average value of the input voltage;
determining the duty ratio of a switching tube for driving the PFC circuit according to the boosting ratio coefficient, the input average current and the input current;
controlling the switching tube to perform switching action according to the duty ratio so as to control the PFC circuit to work;
wherein determining an input average current of the PFC circuit from the input current comprises:
under the condition that the current PFC control period is in the last PFC control period in the current period of the input current, calculating the average current in the current input current period;
and under the condition that the current PFC control period is not in the last PFC control period in the current period of the input current, acquiring the average current of the previous period of the input current.
2. The control method of claim 1, wherein the step-up ratio coefficient ranges from pi/2 to pi.
3. The control method according to claim 1, further comprising:
determining a filtered value of the bus current according to the bus current;
and determining the average value of the input voltage of the PFC circuit according to the bus voltage, the filtered value of the bus current and the input average current.
4. A PFC circuit control apparatus applied to a motor drive circuit including a rectifier circuit, a controller, and an inverter, characterized by comprising:
the input current sampling module is used for collecting the input current of the PFC circuit;
the voltage sampling module is used for collecting bus voltage output by the PFC circuit;
the output current sampling module is used for collecting the bus current output by the PFC circuit;
the controller is configured to:
acquiring the input current of the PFC circuit from the input current sampling module, and determining the input average current of the PFC circuit according to the input current;
acquiring the output current of the PFC circuit from the output current sampling module, acquiring the bus voltage output by the PFC circuit from the voltage sampling module, and determining the average value of the input voltage of the PFC circuit according to the bus voltage, the bus current and the input average current;
determining a boost ratio coefficient according to the given value of the bus voltage and the average value of the input voltage;
determining the duty ratio of a switching tube for driving the PFC circuit according to the boosting ratio coefficient, the input average current and the input current;
controlling the switching tube to perform switching action according to the duty ratio so as to control the PFC circuit to work;
wherein the controller being configured to determine an input average current of the PFC circuit from the input current comprises:
under the condition that the current PFC control period is in the last PFC control period in the current period of the input current, calculating the average current in the current input current period;
and under the condition that the current PFC control period is not in the last PFC control period in the current period of the input current, acquiring the average current of the previous period of the input current.
5. The PFC circuit control apparatus of claim 4, wherein the boost ratio coefficient ranges from pi/2 to pi.
6. The PFC circuit control device of claim 4, wherein the controller is further configured to:
determining a filtered value of the bus current according to the bus current;
and determining the average value of the input voltage of the PFC circuit according to the bus voltage, the filtered value of the bus current and the input average current.
7. A PFC circuit comprising an inductor, a switching tube and a fast recovery diode, characterized in that the PFC circuit further comprises a PFC circuit control device according to any one of claims 4-6;
one end of the inductor is the positive electrode of the input end of the PFC circuit, the other end of the inductor is connected with the input end of the switch tube and the positive electrode of the fast recovery diode in a common mode, the cathode of the fast recovery diode is the positive electrode of the output end of the PFC circuit, the output end of the switch tube is connected with the negative electrode of the output end of the PFC circuit, and the control end of the switch tube is the control end of the PFC circuit.
8. A motor driving circuit, comprising a rectifying module and a filtering module, wherein the motor driving circuit further comprises the PFC circuit of claim 7;
the output end of the rectification module is connected with the input end of the PFC circuit, and the rectification module is used for rectifying alternating current input into the motor driving circuit and outputting pulsating direct current;
the filtering module is connected with the output end of the PFC circuit and used for filtering the direct current output by the PFC circuit and outputting smooth direct current, and the filtering module is connected with a direct current bus and supplies power to the motor driving circuit through the direct current bus.
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