A control method to solve the problem of single-phase PFC input current phase advance under wide frequency conversion

Abstract

The present invention discloses a control method for solving the problem of phase advance of single-phase PFC input current under wide frequency conversion, and belongs to the technical field of power generation, power transformation or power distribution. The method uses a voltage outer loop to adjust the error between the output voltage sampling value and the output voltage reference value to obtain the inductor current peak value, calculates the inductor current reference value according to the inductor current peak value, the input voltage sampling value, and the phase compensation amount, and uses a current inner loop to adjust the error between the inductor current reference value and the inductor current sampling value to obtain the duty cycle change amount, and performs an accumulation operation on the duty cycle change amount and the duty cycle feedforward amount to obtain the actual duty cycle of the single-phase PFC switch tube. The high power factor of the converter under wide frequency conversion of the aviation power grid is achieved by adaptively compensating the input current.

Description

Technical Field

[0001] The present invention relates to power electronics technology, and in particular to a control method for a PFC converter under wide frequency conversion of an aviation power grid. Specifically, a control method for solving the problem of phase advance of a single-phase PFC input current under wide frequency conversion is disclosed, and the invention belongs to the technical field of power generation, power transformation or power distribution. Background Art

[0002] Aviation power grids mainly use two types of AC power supply systems, one is a constant frequency AC system with a frequency of 400Hz, and the other is a variable frequency AC system with a frequency of 360Hz to 800Hz. Since the 21st century, aviation power grids have gradually transitioned from the previous constant frequency AC system to the variable frequency AC system. Compared with the constant frequency AC system, the variable frequency AC system has many advantages. The input voltage frequency varies in a wide range, which makes the power factor correction of aviation power grids very different from the traditional power factor correction on the ground. How to achieve high power factor, reduce input current distortion, and reduce interference to aviation power grids in a wide input voltage frequency range is very important, which puts higher requirements on the power factor correction module of aviation power grids.

[0003] At present, the variable frequency AC system used in passenger aircraft has two voltage levels. For example, the B787 uses a 230V / 360Hz~800Hz variable frequency AC system, the A380 uses a 115V / 360Hz~800Hz variable frequency AC system, and the aircraft AC power supply system used by my country's domestically produced C919 is a 115V / 400Hz constant frequency AC system when it is stable, and a variable frequency AC system when the input voltage frequency of the AC power supply system changes between 360Hz and 800Hz. Therefore, with the increasing application of variable frequency AC systems with wide input frequencies in passenger aircraft AC power supply systems, power factor correction technology has also developed further.

[0004] The traditional active power factor correction circuit Boost PFC generally uses the input filter capacitor to absorb the switching ripple caused by the switching action. Usually, the converter works at the industrial frequency. Since the AC frequency of the input voltage is very low, the amplitude of the current flowing through the input filter capacitor is very small. Although the current flowing into the input filter capacitor leads the input voltage by 90°, due to the small current amplitude, the phase of the input current leading the input voltage can be ignored. However, when the traditional active power factor correction converter is connected to the aviation variable frequency power grid with an input voltage of 360Hz to 800Hz, the amplitude of the current flowing through the input filter capacitor becomes very large, resulting in the problem of input current distortion. The phase difference angle between the input current and the input voltage increases with the increase of the input voltage frequency, and the input current phase lead problem becomes very serious, which also causes the overall power factor of the converter to decrease.

[0005] In view of the current situation that the phase advance problem of traditional Boost PFC connected to aviation variable frequency power grid becomes prominent as the input voltage frequency increases, there are currently three solutions: adding a delay network, duty cycle prediction method, and initial phase angle correction. Adding a delay network is a simple way to solve the problem of input current phase advance. The leading phase of the input current is offset by adding a delay circuit to the input voltage sampling circuit. However, the delay circuit can only achieve a fixed phase angle delay. When the input voltage frequency changes, this solution is no longer applicable. The duty cycle prediction method samples the input voltage, output voltage, input current, inductor current and other characteristic quantities of the main circuit, compares and analyzes the sampled signals, and finally accurately calculates the on-time and off-time of the switch tube, thereby obtaining the ever-changing duty cycle of the switch tube. Compared with the traditional voltage loop plus current loop control method, the duty cycle prediction method omits the error feedback link. Theoretically, there is no input current phase advance caused by the loop, but the calculation process of the duty cycle prediction method is too complicated and the response speed is easily affected by the main circuit parameters and the control circuit. Once the response speed lags behind or is affected by some parasitic parameters that change in the circuit, the calculated value of the duty cycle will be inaccurate, which may lead to poor current tracking effect. In severe cases, the inductor current may oscillate, which may eventually cause system instability and reduce the overall reliability. The initial phase angle correction method is a method of adjusting the reference current according to the zero-crossing time of the input voltage and input current. In the traditional average current control, the input current leads the input voltage when the input voltage frequency increases, and the higher the input voltage frequency, the greater the phase of the input current leading. The initial phase angle correction method determines the angle of the input current leading the input voltage by detecting the time difference between the input voltage zero-crossing time and the input current zero-crossing time, and then adjusts the phase angle difference between the reference current and the input voltage by looking up the sine table to offset the phase advance of the input current. However, the average current control method only determines the phase difference between the input current and the input voltage based on the time difference between the zero-crossing points of the input current and the input voltage, which is somewhat one-sided, and the accuracy of this detection method is not very high. At the same time, the programming is relatively complicated, and it only weakens the phase advance of the input current, but cannot be fundamentally eliminated.

[0006] The method proposed in this paper can adjust the compensation amount in real time according to the input voltage frequency, so as to achieve the best compensation effect even when the voltage frequency changes. Moreover, it is simple to implement and does not require complicated calculations. Summary of the invention

[0007] The purpose of the present invention is to address the deficiencies of the above-mentioned background technology and provide a control method for solving the problem of single-phase PFC input current phase lead under wide frequency conversion, adjust the reference current phase compensation amount in real time according to the change of input voltage frequency, achieve the purpose of the invention of improving the power factor of the converter under wide frequency conversion input voltage, and solve the technical problem of input current phase lead under wide frequency conversion input voltage.

[0008] The present invention adopts the following technical solutions to achieve the above-mentioned invention object:

[0009] A control method to solve the problem of single-phase PFC input current phase advance under wide frequency conversion.

[0010] The voltage outer loop is used to adjust the error between the output voltage sampling value and the output voltage reference value to obtain the inductor current peak value;

[0011] The inductor current reference value is calculated based on the inductor current peak value, input voltage sampling value, and phase compensation value θ. Where C is the capacitance of the input filter capacitor, f is the frequency of the input voltage, V rms is the effective value of the input voltage, P in is the input power;

[0012] The current inner loop is used to adjust the error between the inductor current reference value and the inductor current sampling value to obtain the duty cycle change;

[0013] The duty cycle variation and the duty cycle feedforward are accumulated to obtain the actual duty cycle of the single-phase PFC switch tube.

[0014] As a further optimization solution to the control method of single-phase PFC input current phase advance under wide frequency conversion, the input voltage frequency detection method is:

[0015] Sampling the input voltage and taking the absolute value of the input voltage sampling signal;

[0016] Selecting a first hysteresis comparison value and a second hysteresis comparison value for judging whether the absolute value of the input voltage sampling signal at the current moment is within a half-wave or within a dead zone, wherein the first hysteresis comparison value is greater than the second hysteresis comparison value;

[0017] When the absolute value of the input voltage sampling signal at the current moment is within the half-wave, the initialization timer starts counting, and ends counting when the absolute value of the input voltage sampling signal is within the dead zone for the first time at the next moment and thereafter. The time from the start of the counter counting to the end of the counting is the time of each half-wave.

[0018] The frequency of the input voltage is inverted according to the time of each half-wave.

[0019] As a further optimized solution for a control method to solve the problem of the leading phase of the input current of single-phase PFC under wide frequency variation, the specific method for determining whether the absolute value of the input voltage sampling signal at the current moment is within the half-wave or the dead zone is as follows: when the absolute value of the input voltage sampling signal at the current moment is greater than the first hysteresis comparison value, the absolute value of the input voltage sampling signal at the current moment is within the half-wave; when the absolute value of the input voltage sampling signal at the current moment is less than the second hysteresis comparison value, the absolute value of the input voltage sampling signal at the current moment is within the dead zone.

[0020] As a further optimized solution for a control method to solve the problem of the leading phase of the input current of single-phase PFC under wide frequency variation, the expression for inverting the frequency of the input voltage according to the time of each half-wave is: f = 1 / (2nt), where n is the count value of the counter, t is the time of each switching period, and nt represents the time of each half-wave.

[0021] A control system for a control method to solve the problem of the leading phase of the input current of single-phase PFC under wide frequency variation includes:

[0022] A first accumulator, one input terminal of which is connected to the output voltage sampling value, and the other input terminal of which is connected to the output voltage reference value, to calculate the error between the output voltage sampling value and the output voltage reference value;

[0023] A voltage outer loop, the input terminal of which is connected to the output terminal of the first accumulator. After adjusting the error between the output voltage sampling value and the output voltage reference value, it outputs the peak value of the inductor current;

[0024] A calculation unit, the input terminals of which are connected to the peak value of the inductor current, the input voltage sampling value, the capacitance value of the input filter capacitor, the frequency of the input voltage, the effective value of the input voltage, and the input power. It calculates the phase compensation amount according to the capacitance value of the input filter capacitor, the frequency of the input voltage, the effective value of the input voltage, and the input power, and calculates the inductor current reference value according to the peak value of the inductor current, the input voltage sampling value, and the phase compensation amount;

[0025] A second accumulator, one input terminal of which is connected to the inductor current reference value, and the other input terminal of which is connected to the inductor current sampling value, to calculate the error between the inductor current reference value and the inductor current sampling value;

[0026] A current inner loop, the input terminal of which is connected to the output terminal of the second accumulator. After adjusting the error between the inductor current reference value and the inductor current sampling value, it outputs the duty cycle variation; and,

[0027] A third accumulator, one input terminal of which is connected to the output terminal of the current inner loop, and the other input terminal of which is connected to the duty cycle feedforward amount, and outputs the actual duty cycle of the single-phase PFC switching tube.

[0028] As a further optimization solution for the control system of the control method for solving the phase advance of the single-phase PFC input current under wide frequency conversion, the frequency of the input voltage is realized by a software algorithm stored in a computer storage medium.

[0029] The present invention adopts the above technical solution and has the following beneficial effects: the present invention proposes a method for adaptive phase compensation of input current, and calculates the instantaneous phase compensation amount for determining the reference value of the inductor current by measuring the input voltage frequency in real time. The instantaneous phase compensation amount is simple to obtain and does not require complicated calculations. The single-phase PFC switch tube control signal is obtained according to the phase compensation method proposed in the present invention, which can make the input current follow the input voltage well when the input voltage frequency changes in a wide frequency range of 360Hz to 800Hz, thereby realizing a high power factor of the converter under wide frequency conversion of the aviation power grid, and at the same time reducing the distortion of the input current and reducing interference to the aviation power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the schematic diagram of the input current phase lead caused by the input filter capacitor.

[0031] FIG2(a) is a phase relationship vector diagram of the input current, the inductor current and the current on the input filter capacitor when the current on the input filter capacitor is not compensated. FIG2(b) is a phase relationship vector diagram of the input current, the inductor current and the current on the input filter capacitor after phase compensation.

[0032] Figure 3 It is the actual waveform diagram between the input voltage, the current on the input filter capacitor, the input current in the ideal case and the reference current under the adaptive phase compensation control.

[0033] Figure 4 This is a schematic diagram of the principle of measuring input voltage frequency according to the present invention.

[0034] Figure 5 The present invention implements the proposed control method for solving the problem of single-phase PFC input current phase advance under wide frequency conversion. DETAILED DESCRIPTION

[0035] The technical solution of the invention is described in detail below with reference to the accompanying drawings:

[0036] The principle of input current phase advance caused by filter capacitor is as follows Figure 1 shown.

[0037] Assuming the input voltage is a standard sinusoidal voltage, it can be expressed as:

[0038]

[0039] Among them, Vin (t) is the input voltage, V rms is the effective value of the input voltage, and f is the frequency of the input voltage.

[0040] According to the relationship between the current and voltage flowing through the capacitor, the current i flowing through the input filter capacitor can be calculated. c (t):

[0041]

[0042] Where C is the input filter capacitor and dt is the differential of time t.

[0043] Then, the input current i ac (t) can be calculated by the current i flowing through the input filter capacitor c (t) plus the current i flowing through the inductor L (t) It is concluded that:

[0044] i ac (t) = i L (t)+i c (t) (3)

[0045] According to the above theoretical analysis, the phase lead of the input current is mainly caused by the input filter capacitor, and the current on the input filter capacitor has a greater impact on the input current phase lead when the input voltage frequency increases. Therefore, the solution is studied below based on the phase relationship vector diagram of the current on the input filter capacitor, the input current, and the inductor current shown in Figure 2.

[0046] When the current on the input filter capacitor is not compensated, the phase relationship vector diagram between the input current, inductor current and filter capacitor current is shown in Figure 2(a). After phase compensation, the phase relationship vector diagram between the three is shown in Figure 2(b). Since the current on the input filter capacitor changes with the input voltage frequency and input voltage amplitude, it is necessary to adjust the current according to the input voltage frequency f and amplitude V. rms To adjust the size of θ in real time to achieve the best effect.

[0047] The actual waveforms of the input voltage, the current on the filter capacitor, the input current and the reference current under the adaptive phase compensation control are as follows: Figure 3 As shown, the specific mathematical relationship is as follows:

[0048] Taking the input voltage as the reference, the effective value of the AC input voltage is V rms , the instantaneous value of the AC input voltage can be expressed as:

[0049]

[0050] Assuming the power factor is 1, the instantaneous value of the input current i ideal (t) can be expressed as:

[0051]

[0052] Among them, P in is the input power.

[0053] Ideally, the AC current flowing through the input filter capacitor can be calculated as follows:

[0054]

[0055] Assume that the reference current i of the inductor current required under ideal conditions is ref The expression of (t) is:

[0056] i ref (t) = I ref ·sin(2πft-θ) (7)

[0057] Where θ is the phase compensation amount, I ref is the amplitude of the reference current.

[0058] Assuming that the bandwidth of the designed current loop is high enough, the inductor current can completely keep up with the current reference value, that is:

[0059] i L (t) = i ref (t) (8)

[0060] According to KCL, the input current is equal to the inductor current plus the current on the filter capacitor:

[0061] i ideal (t) = i L (t)+i c (t) (9)

[0062] Substituting equations (5), (6), (7), and (8) into equation (9), we can obtain:

[0063]

[0064] Solve the above equation:

[0065]

[0066]

[0067] It can be further calculated that:

[0068]

[0069]

[0070] so:

[0071]

[0072] From the above relationship, it can be seen that in order to achieve a power factor close to 1, the phase compensation amount θ must be adjusted in real time with the frequency of the input voltage, so the input voltage information needs to be detected in real time. The present invention discloses a software algorithm for detecting the input voltage frequency, and the error is within the allowable range, which can be actually applied.

[0073] The frequency of the input voltage is detected by software. The specific process is:

[0074] Step 1: Take the absolute value of the sampled sinusoidal input voltage signal and get Figure 4 The input voltage sampling value of the half-wave sine signal shown is V in |.

[0075] Step 2: Set two hysteresis comparison values ​​V through the program H and V L It can be judged whether the current moment is within the half wave or the dead zone. When the sinusoidal half wave signal |V in |Greater than comparison value V H It means that the input voltage sampling signal at the current moment is within the half wave. When the sinusoidal half wave signal |V in |Less than comparison value V L It indicates that the input voltage sampling signal at the current moment is within the dead zone.

[0076] Step 3: When the input voltage sampling signal is within the half-wave at the current moment, initialize counter i to zero and start counting. When the input voltage sampling signal is within the dead zone for the first time at the next moment and thereafter, the counting operation of the counter ends. The time from the start of counting to the end of counting corresponds to the time of one switching cycle.

[0077] Step 4: It is known that the time t of each switching cycle is 6.67us. Multiplying it by the counter count value n can get the time of each half wave, and then get the input voltage frequency f=1 / (2nt).

[0078] In order to achieve the function of power factor correction, the traditional Boost PFC circuit structure is a diode rectifier bridge plus a Boost boost circuit. There is only one switch tube in the entire circuit. Therefore, we only need to control the switch tube to control the inductor current and make it track the input voltage, thereby achieving the purpose of power factor correction.

[0079] The architecture for implementing the control algorithm of the present invention is as follows Figure 5As shown in the figure, a duty cycle feedforward control scheme including voltage loop and current loop is used. First, the output voltage sampling value V o With the output voltage reference value V ref The error is V err The reference current amplitude I is sent to the voltage outer loop M , and then according to the reference current amplitude I M and the input voltage sampling value |V in | and the compensation phase quantity θ to obtain the inductor current reference value I ref , inductor current reference value I ref The sampling value of the inductor current I L The current error I is obtained by subtracting err The duty cycle change Δd is obtained by sending it into the current loop. The duty cycle change Δd and the duty cycle feedforward amount D are added together to obtain the actual duty cycle d, which is the control method of the control system.

[0080] In summary, the protection scope of the present invention is not limited to the above embodiments, and all technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A control method to solve the problem of single-phase PFC input current phase advance under wide frequency conversion. It is characterized in that The voltage outer loop is used to adjust the error between the output voltage sampling value and the output voltage reference value to obtain the inductor current peak value; The inductor current reference value is calculated based on the inductor current peak value, input voltage sampling value, and phase compensation value θ. Where C is the capacitance of the input filter capacitor, f is the frequency of the input voltage, V rms is the effective value of the input voltage, P in is the input power; The current inner loop is used to adjust the error between the inductor current reference value and the inductor current sampling value to obtain the duty cycle change; The duty cycle variation and the duty cycle feedforward are accumulated to obtain the actual duty cycle of the single-phase PFC switch tube.

2. According to claim 1, a control method for solving the problem of single-phase PFC input current phase leading under wide frequency conversion, It is characterized in that The method for detecting the frequency of the input voltage is: Sampling the input voltage and taking the absolute value of the input voltage sampling signal; Selecting a first hysteresis comparison value and a second hysteresis comparison value for judging whether the absolute value of the input voltage sampling signal at the current moment is within a half-wave or a dead zone, wherein the first hysteresis comparison value is greater than the second hysteresis comparison value; When the absolute value of the input voltage sampling signal at the current moment is within the half-wave, the initialization timer starts counting, and ends counting when the absolute value of the input voltage sampling signal is within the dead zone for the first time at the next moment and thereafter. The time from the start of the counter counting to the end of the counting is the time of each half-wave. The frequency of the input voltage is inverted according to the time of each half-wave.

3. According to claim 2, a control method for solving the problem of single-phase PFC input current phase leading under wide frequency conversion, It is characterized in that The specific method for judging whether the absolute value of the input voltage sampling signal at the current moment is within the half-wave or the dead zone is as follows: when the absolute value of the input voltage sampling signal at the current moment is greater than the first hysteresis comparison value, the absolute value of the input voltage sampling signal at the current moment is within the half-wave; when the absolute value of the input voltage sampling signal at the current moment is less than the second hysteresis comparison value, the absolute value of the input voltage sampling signal at the current moment is within the dead zone.

4. According to claim 2, a control method for solving the problem of single-phase PFC input current phase leading under wide frequency conversion, It is characterized in that The expression for the frequency of the input voltage according to the time inversion of each half-wave is: f=1 / (2nt), wherein n is the count value of the counter, t is the time of each switching cycle, and nt represents the time of each half-wave.

5. A control system for implementing a control method for solving the problem of single-phase PFC input current phase leading under wide frequency conversion as described in any one of claims 1 to 4, It is characterized in that include: A first accumulator, one input terminal of which is connected to the output voltage sampling value, and the other input terminal of which is connected to the output voltage reference value, is used to calculate the error between the output voltage sampling value and the output voltage reference value; A voltage outer loop, whose input end is connected to the output end of the first accumulator, outputs the inductor current peak value after adjusting the error between the output voltage sampling value and the output voltage reference value; A calculation unit, whose input terminal is connected to the inductor current peak value, the input voltage sampling value, the capacitance of the input filter capacitor, the frequency of the input voltage, the effective value of the input voltage, and the input power, calculates the phase compensation amount according to the capacitance of the input filter capacitor, the frequency of the input voltage, the effective value of the input voltage, and the input power, and calculates the inductor current reference value according to the inductor current peak value, the input voltage sampling value, and the phase compensation amount; A second accumulator, one input terminal of which is connected to the inductor current reference value, and the other input terminal of which is connected to the inductor current sampling value, is used to calculate the error between the inductor current reference value and the inductor current sampling value; The current inner loop has an input terminal connected to the output terminal of the second accumulator, and outputs a duty cycle variation after adjusting the error between the inductor current reference value and the inductor current sampling value; and, The third accumulator has one input terminal connected to the output terminal of the inner current loop and the other input terminal connected to the duty cycle feedforward quantity, and outputs the actual duty cycle of the single-phase PFC switch tube.

6. A control system for solving the control method of single-phase PFC input current phase advance under wide frequency conversion according to claim 5, It is characterized in that The frequency of the input voltage is implemented by a software algorithm stored on a computer storage medium.

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