Low-cost power factor correction system and method for AC-DC converters

Abstract

This invention discloses a low-cost power factor correction system and method for AC-DC converters. The system includes: a sampling module that acquires the instantaneous values ​​of the converter's input current and output voltage through a sampling resistor; a slope calculation module that calculates the rising and falling slopes of the input inductor excitation current and outputs the results to a PWM output module, while simultaneously calculating the instantaneous input voltage value and transmitting it to a target current calculation module; a power adjustment module that determines the power adjustment coefficient and inputs it to the target current calculation module; a target current calculation module that calculates the target average input current for the next switching cycle of the converter and feeds it back to the slope calculation module; and a PWM output module that obtains the control signals for switching transistors on and off from the slope calculation module. This invention eliminates the input voltage sampling circuit, simplifies the circuit topology, reduces the number of input signals to the control circuit, and achieves high power factor correction.

Description

Technical Field

[0001] This invention relates to the field of power factor correction technology in AC-DC converters, and more specifically to a low-cost power factor correction system and method for AC-DC converters. Background Technology

[0002] With the increasing demands for energy efficiency and environmental protection from the state, relevant national regulations clearly stipulate that power supply equipment exceeding a certain power level must have power factor correction functionality. This regulation aims to improve overall energy utilization efficiency, reduce grid losses, enhance voltage quality, reduce losses in various equipment, and meet increasingly stringent environmental standards.

[0003] In applications requiring high power factor correction or a wide input voltage range, real-time and accurate acquisition of input voltage values ​​is crucial. Taking power factor correction as an example, its core objective is to ensure that the input current closely follows the waveform and phase of the input voltage, thereby guaranteeing efficient energy utilization. To achieve this goal, the system needs to acquire the input AC voltage and extract key information such as voltage amplitude, frequency, and phase.

[0004] Traditional methods typically rely on sampling circuits to obtain input voltage information and then process the input voltage using ADC devices or analog multiplier circuits to provide comprehensive information support for subsequent control algorithms. However, high-precision ADC devices are not only expensive, but their high-speed sampling and high-precision characteristics are also uneconomical in practical applications of switching power supply input voltage sampling. Furthermore, high-precision, high-speed ADCs or analog circuits increase the complexity of the algorithm or the circuit system, which increases the design complexity and circuit cost of the switching converter. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost power factor correction system and method that achieves power factor correction for AC-DC switching power supplies with a simpler circuit structure, making it suitable for cost-sensitive applications.

[0006] To address the problems of high cost, complex control, and complex circuitry associated with traditional sampling methods, this invention proposes a method that eliminates the need for direct input voltage sampling. This method achieves high power factor correction by sampling only the input current and output voltage. This invention will be described based on a Boost-PFC converter (the applicable circuit structures include, but are not limited to, Boost-PFC converters), where the Boost-PFC operates in CRM mode (critical current mode). In this method, a sampling resistor is connected in series before the inductor in the traditional structure to obtain the inductor current information. The main components used are a DAC and a comparator.

[0007] The technical solution to achieve the purpose of this invention is as follows:

[0008] A low-cost power factor correction system for AC-DC converters, forming a closed-loop circuit with the converter, characterized in that it includes:

[0009] The sampling module acquires the instantaneous values ​​of the converter's input current and output voltage through a sampling resistor. The instantaneous value of the input current is transmitted to the slope calculation module, and the instantaneous value of the output voltage is transmitted to the power adjustment module.

[0010] The slope calculation module is used to calculate the rising and falling slopes of the input inductor excitation current and output them to the PWM output module. At the same time, it calculates the instantaneous value of the input voltage and transmits it to the target current calculation module.

[0011] The power adjustment module is used to determine the power adjustment coefficient, which is then input to the target current calculation module.

[0012] The target current calculation module is used to calculate the target average input current of the converter in the next switching cycle and feed it back to the slope calculation module.

[0013] The PWM output module obtains the control signals for turning on and off the switching transistors from the slope calculation module to perform closed-loop power factor control of the converter.

[0014] Furthermore, the converter is a Boost-PFC converter.

[0015] Furthermore, the instantaneous values ​​of the input current and output voltage output by the sampling module are as follows:

[0016]

[0017] Among them, I c (t) represents the instantaneous value of the input current, V o (t) represents the instantaneous value of the output voltage, V osense (t) represents the instantaneous value of the output sampling resistor voltage, V sense (t) represents the instantaneous value of the input current sampling resistor voltage.

[0018] Furthermore, the slope calculation module includes two comparators and two digital-to-analog converters. The positive terminal of the first comparator is connected to the sampling module, and the negative terminal is connected to the first digital-to-analog converter. The positive terminal of the second comparator is connected to the sampling module, and the negative terminal is connected to the second digital-to-analog converter.

[0019] Furthermore, the rising slope and the falling slope are:

[0020]

[0021] Where k1 and k2 are the rising and falling slopes of the inductor excitation current, respectively, and T s For clock cycles, N1 and N2 are count values. When the drive signal changes from 0 to 1, the counter is 0. When the rising edge of the first comparator is detected, the counter starts counting; when the rising edge of the second comparator is detected, the counter stops counting, and the count value is N1. When the falling edge of the second comparator COMP2 is detected, the counter starts counting; when the falling edge of the first comparator is detected, the counter stops counting, and the count value is N2. a (n) is the target input current output by the target current calculation module in the previous switching cycle.

[0022] Furthermore, the instantaneous value of the input voltage is:

[0023]

[0024] Furthermore, the input to the power adjustment module is the target reference voltage V. ref and the instantaneous value of the output voltage V o (t), the power adjustment coefficient m is determined by the PID control algorithm.

[0025] Furthermore, the target average input current for the next switching cycle is:

[0026] I a (n+1)=mV g (t)

[0027] Where m is the power adjustment coefficient.

[0028] A low-cost power factor correction method based on the system, comprising:

[0029] The instantaneous values ​​of the converter's input current and output voltage are collected by the sampling module. The instantaneous value of the input current is transmitted to the slope calculation module, and the instantaneous value of the output voltage is transmitted to the power adjustment module.

[0030] The slope calculation module calculates the rising and falling slopes of the excitation current and outputs them to the PWM output module. At the same time, it calculates the instantaneous value of the input voltage and passes it to the target current calculation module.

[0031] The power adjustment module determines the power adjustment coefficient and inputs it to the target current calculation module;

[0032] The target current calculation module calculates the target reference current for the next switching cycle;

[0033] The PWM output module outputs PWM drive outputs and obtains control signals for turning the switching transistors on and off from the slope calculation module, thereby controlling the switching transistors of the converter to turn on and off.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention removes the traditional input voltage sampling circuit, simplifies the circuit topology and reduces the number of input signals of the control circuit, and achieves high power factor correction; the present invention can achieve high power factor correction of AC-DC converters without directly sampling the input voltage, and can achieve input voltage sampling without relying on high-cost, high-precision, high-speed ADC devices or other complex sampling devices, thereby reducing the cost of the converter and providing an economical, efficient and reliable solution for power factor correction of AC-DC switching power supplies, especially suitable for cost-sensitive application scenarios. Attached Figure Description

[0035] Figure 1 This is a circuit diagram of the Boost-PFC topology.

[0036] Figure 2 This is the module transfer diagram of Boost-PFC.

[0037] Figure 3 This is a schematic diagram of the slope calculation waveform.

[0038] Figure 4 This is the flowchart of the control algorithm of the present invention. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] To address the problems of high cost, complex control, and complex circuitry associated with traditional sampling methods, this invention proposes a method that eliminates the need for direct input voltage sampling. This method achieves high power factor correction by sampling only the input current and output voltage. This invention will be described based on a Boost-PFC converter (the applicable circuit structures include, but are not limited to, Boost-PFC converters), where the Boost-PFC operates in CRM mode (critical current mode). In this method, a sampling resistor is connected in series before the inductor in the traditional structure to obtain the inductor current information. The main components used are a DAC and a comparator.

[0041] Combination Figure 1 Taking the Boost-PFC converter as an example, its input is AC and its output is DC. This invention is not limited to the Boost topology; any AC-DC converter that needs to acquire input voltage and realize power factor correction is within the scope of this invention. Figure 1This includes a circuit diagram of a Boost-PFC converter. The positive input terminal of the rectifier bridge is connected to the positive terminal of the input capacitor, and the negative input terminal of the rectifier bridge is connected to the input ground. The input capacitor C... in The negative terminal is connected to the input ground, and the positive terminal of the input capacitor is connected to the sampling resistor R. sense One end is connected, sampling resistor R sense The other end is connected to one end of the Boost inductor L, and the other end of the inductor L is connected to the sampling resistor R. sense Sampling resistor R sense The other end is connected to the positive terminal of the freewheeling diode D1, while the drain of the switching transistor S1 is connected to the positive terminal of the diode D1, and the source is grounded. The negative terminal of the diode D1 is connected to the output filter capacitor C. o The positive terminal is connected to the output filter capacitor C. o The negative terminal is connected to ground, and the load R o The two ends are connected to the positive and negative terminals of the output capacitor, respectively, and the load R is... o A sampling resistor R is connected in parallel across both ends. s1 With R s2 , where R s1 With R s2 This indicates a series connection.

[0042] Figure 2 The diagram shows the control system modules for Boost-PFC, which consist of five sub-modules: sampling module, power adjustment module, slope calculation module, target current calculation module, and PWM output module.

[0043] The input current and output voltage sampling module acquires the instantaneous value V of the input current sampling resistor voltage. sense (t) and the instantaneous value of the output sampling resistor voltage V osense (t), instantaneous value of input and output current I c (t) and the instantaneous value of the output voltage V o (t), where the instantaneous value of the input current I c (t) is passed to the slope calculation module, and the instantaneous voltage value V is output. o (t) is passed to the power adjustment module. The relationship between the input current sample value, the output voltage sample value and the actual value can be expressed by the following formula.

[0044]

[0045] The slope calculation module includes two comparators, COMP1 and COMP2, and two digital-to-analog converters, DAC1 and DAC2. The positive terminal of comparator COMP1 is connected to the sampling resistor voltage V. sense The negative terminal is connected to DAC1; the positive terminal of COMP2 is connected to the sampling resistor voltage V. sense The negative terminal is connected to DAC2.

[0046] The slope calculation module calculates the rising slope k1 and falling slope k2 of the input current based on the comparator output. The input to the slope calculation module is the instantaneous value I of the input current. c (t) and target reference average current I s (n) This module will calculate the rising slope k1 and falling slope k2 of the input inductor excitation current respectively (if the current does not have a falling range, such as when Flyback is operating in CCM mode, an excitation current recovery module will be added to restore the primary excitation current of the transformer). For AC-DC switching converters, the rising slope k1 and falling slope k2 of the input excitation current are usually equal to the input voltage V. g (t), Output voltage V o (t) and the excitation inductance L are functions. It can be expressed as follows:

[0047]

[0048] Suppose that the target input current for this switching cycle has been calculated in the previous switching cycle as I. a (n), then according to the Boost-PFC operating in CRM mode, the peak inductor current of this switching cycle is 2, I. a (n), then the two signals output by the DAC must be between 0 and 2, I a The range is between (n), therefore the DAC output quantity selected by this method is as follows:

[0049]

[0050] Different duty cycles can be obtained from the two comparison signals of the comparator. When the drive signal changes from 0 to 1, the time counter CLK_POS is set to 0. When the rising edge of comparator COMP1 is detected, the counter CLK_POS starts counting, and when the rising edge of comparator COMP2 is detected, the counter CLK_POS stops counting. Assuming the system clock period is Ts and the count value of CLK_POS in this device is N1, the rising slope k1 can be calculated as follows:

[0051]

[0052] When the drive signal changes from 0 to 1, the time counter CLK_NEG is set to 0. When a falling edge of comparator COMP2 is detected, the counter CLK_NEG starts counting, and when a falling edge of comparator COMP1 is detected, the counter CLK_NEG stops counting. Let the system clock period be T. s If the count value of CLK_NEG on this device is N2, then the rising slope k2 can be calculated as follows:

[0053]

[0054] In equation (1.5) above, V o (t) represents the known quantity obtained from sampling. The rising slope k1 and falling slope k2 of the input current can be obtained through a DAC and a comparator. The instantaneous value of the input voltage V can be obtained by solving the above equation. g (t) is shown below. The instantaneous value of the input voltage is passed to the target current calculation module.

[0055]

[0056] The input to the power adjustment module is the target reference voltage V. ref and the instantaneous value of the output voltage V o The converter (t) employs a PID control algorithm, and its output is the power adjustment coefficient m. m reflects the magnitude of the input current and is used to regulate the converter's power. The power adjustment coefficient m is ultimately transmitted to the target current calculation module.

[0057] The target current calculation module receives the instantaneous value of the input voltage V as input. g (t) and the power adjustment coefficient m, for different converters and operating modes, can be used to obtain the target average input current I for the next switching cycle through corresponding calculations. s (n+1). Target reference average current I s (n+1) will be passed to the slope calculation module.

[0058] I a (n+1)=mV g (t)(1.10)

[0059] The input to the PWM output module is the control signal from the slope calculation module. The drive control signal for the switching transistor is generated by the slope calculation module, which contains two counters, dutyon_clk and dutyoff_clk. The dutyoff_clk counter starts counting when the drive signal is turned on. When the count value equals 2N1, it outputs the dutyoff control signal to turn off the switching transistor and simultaneously resets the counter to 0. At this point, dutyon_clk starts counting, and when the count value equals 2N2, it outputs the dutyon control signal to turn on the switching transistor and simultaneously resets the counter to 0. The PWM output module turns the switching transistor on and off according to the control signal from the slope calculation module, ultimately achieving high power factor closed-loop control of the AC-DC converter without direct sampling of the input voltage.

[0060] Figure 3 This is a schematic diagram for calculating the inductor current slope. The Boost-PFC converter, operating in CRM mode, can naturally achieve PFC and can be used for power factor correction. Inductor L operating in CRM mode can achieve an ideal PF value (PF = 1).

[0061] As can be seen from the figure, since the target input current for this switching cycle, I, was calculated in the previous switching cycle, this is already the target input current for the current switching cycle. a (n), therefore the peak inductor current of this switching cycle is 2, I a (n), the two DC outputs of the DAC module intersect with the voltage on the sampling resistor to form two square wave signals.

[0062] Figure 4 This is a flowchart of the low-cost power factor correction method of the present invention. The specific calculation steps can be divided into the following steps:

[0063] Step 1: The DAC in the slope calculation module outputs two DC voltages;

[0064] Step 2: Calculate the slopes k1 and k2 of the restored excitation current on the primary side;

[0065] Step 3: Input voltage V g (t) Calculation;

[0066] Step 4: Calculation of the power adjustment coefficient m;

[0067] Step 5: Target reference current I for the next switching cycle a Calculate (n+1);

[0068] Step 6: PWM drive output.

[0069] This embodiment also provides a computer storage medium storing an executable program, which is executed by a processor to implement the steps of the low-cost power factor correction method.

[0070] This invention can sample input voltage values ​​without relying on high-cost, high-precision, high-speed ADC devices or other complex sampling devices, thereby reducing the cost of the converter.

[0071] The method described herein encompasses all the technical features of the corresponding system, which will not be repeated here. The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. The present invention described herein can have many variations; for example, obtaining slope information can be achieved using a single-channel DAC as described, or a two-channel DAC method, etc. Such variations should not deviate intentionally from the spirit and scope of the present invention. Therefore, all modifications that are obvious to those skilled in the art are included within the scope of the claims.

Claims

1. A low cost power factor correction system for an AC-DC converter, forming a closed loop with the converter, characterized in that, The application relates to a low-cost power factor correction method and device. The sampling module collects the input current instantaneous value and the output voltage instantaneous value through a sampling resistor, the input current instantaneous value is transmitted to a slope calculation module, and the output voltage instantaneous value is transmitted to a power adjustment module; a slope calculation module for calculating the rising slope and the falling slope of the input inductance excitation current, outputting to the PWM output module, and simultaneously calculating the input voltage instantaneous value V g (t) is transmitted to the target current calculation module; The power adjustment module is used for determining a power adjustment coefficient and inputting the power adjustment coefficient into a target current calculation module; The target current calculation module is used for calculating a target input average current of a next switching period of the converter and feeding back the target input average current to the slope calculation module; The PWM output module obtains the control signals of the switch tube opening and closing from the slope calculation module and carries out power factor closed-loop control of the converter. The rising slope and the falling slope are: Wherein, k1, k2 are the rising slope and the falling slope of the inductive excitation current, respectively, T s is the clock period, N1, N2 are the count values, the counter is 0 when the driving signal changes from 0 to 1, the counter starts counting when the rising edge of the first comparator is detected, the counter stops counting when the rising edge of the second comparator is detected, and the count value is N1; the counter starts counting when the falling edge of the second comparator COMP2 is detected, the counter stops counting when the falling edge of the first comparator is detected, and the count value is N2, I a (n) is the target input current output by the target current calculation module in the last switching period; The input voltage instantaneous value is: The input of the power adjustment module is a target reference voltage V ref and an output voltage instantaneous value V o (t), and the power adjustment coefficient m is determined by a PID control algorithm. The target input average current of the next switching period is: I a (n+1) = mV g (t) Wherein, m is the power adjustment coefficient.

2. A low cost power factor correction system for an AC-DC converter as claimed in claim 1, characterized in that, The converter is a Boost-PFC converter.

3. A low cost power factor correction system for an AC-DC converter as claimed in claim 2, wherein, The input current instantaneous value and the output voltage instantaneous value output by the sampling module are: Wherein, I c (t) is the input current instantaneous value, V o (t) is the output voltage instantaneous value, V osense (t) is the output sampling resistance voltage instantaneous value, V sense (t) is the input current sampling resistance voltage instantaneous value, sampling resistance R s1 And R s2 In series and in parallel on both ends of the load, sampling resistance R sense One end is connected with the positive end of the input capacitor, and the other end is connected with one end of the Boost inductor.

4. A low cost power factor correction system for an AC-DC converter as claimed in claim 2, wherein, The slope calculation module comprises two comparators and two digital-analog converters, the positive terminal of the first comparator is connected with the sampling module, the negative terminal of the first comparator is connected with the first digital-analog converter; the positive terminal of the second comparator is connected with the sampling module, and the negative terminal of the second comparator is connected with the second digital-analog converter.

5. A low cost power factor correction method based on the system of any of claims 1-4, characterized by, The application relates to a low-cost power factor correction method and device. The sampling module collects the input current instantaneous value and the output voltage instantaneous value through a sampling resistor, the input current instantaneous value is transmitted to a slope calculation module, and the output voltage instantaneous value is transmitted to a power adjustment module; The slope calculation module calculates the rising slope and the falling slope of the excitation current and outputs the rising slope and the falling slope to a PWM output module, and simultaneously calculates the input voltage instantaneous value and transmits the input voltage instantaneous value to a target current calculation module; The power adjustment module is used for determining a power adjustment coefficient and inputting the power adjustment coefficient into a target current calculation module; The target current calculation module is used for calculating a target input average current of a next switching period of the converter and feeding back the target input average current to the slope calculation module; The PWM output module obtains the control signals of the switch tube opening and closing from the slope calculation module and carries out power factor closed-loop control of the converter.

6. A computer storage medium, characterized in that The computer storage medium stores an executable program, and the executable program is executed by a processor to realize the steps of the low-cost power factor correction method in claim 5.

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