A high-frequency control method for three-phase active APFC based on impulse equivalent principle

Abstract

The present invention proposes a three-phase active APFC high-frequency control method based on the impulse equivalent principle, including the following steps: 1. Obtaining the voltage amplitude, frequency and phase information of the power grid; 2. Performing DQ rotation coordinate transformation on the three-phase input current; 3. Obtaining the output DC voltage information; 4. Performing closed-loop feedback control in the DQ coordinate system to calculate the three-phase modulation signal; 5. Multiplying the three-phase modulation signal and the carrier signal by the same proportional coefficient K (K≤1) to obtain a high-frequency pulse equivalent to the initial pulse impulse; 6. Using the regular sampling method to calculate the PWM drive signal to drive the main switch tube. The high-frequency control method proposed by the present invention is applicable to all PWM converters, can greatly reduce the volume and weight of the converter, and the system works stably and reliably.

Description

Technical Field

[0001] The invention relates to the technical field of high power factor rectification, and in particular to a three-phase active APFC high-frequency control method based on the impulse equivalent principle. Background Art

[0002] With the development of power electronics technology, high-power PWM chopper switching power supplies have been widely used. In the current power supply mode, a two-stage architecture is generally used: the front stage is an AC / DC rectifier power supply, which provides a stable DC bus voltage to the back stage; the back stage is a distributed DC / DC power supply, which provides power to the load. In engineering design, in order to improve the power factor on the input side of the power grid and reduce the harmonic content of the input current, the front stage rectifier power supply generally adopts three-phase active APFC technology.

[0003] Many experts and scholars have conducted in-depth research on three-phase APFC technology. At present, DSP is mainly used to implement the following control method: sampling three-phase input current and DC output voltage, performing DQ rotation coordinate system transformation on the three-phase input current, and performing error adjustment in the DQ coordinate system to obtain the controlled active and reactive vectors, and then obtain the three-phase AC signal through inverse coordinate transformation. As mentioned above, the three-phase APFC control algorithm requires a large number of mathematical operations, and its switching frequency cannot be effectively improved due to the limited computing speed of DSP.

[0004] In some fields (such as military fields), the requirements for volume and weight are very strict. In the design of switching power supplies, the most effective way to reduce volume and weight is to increase the switching frequency. Therefore, a new control method is needed to achieve high-frequency control of three-phase active APFC. Summary of the invention

[0005] The technical problems to be solved by the present invention are:

[0006] The purpose of the present invention is to propose a three-phase active APFC high-frequency control method based on the impulse equivalent principle based on the computing power of the current PWM digital processor. By converting a single drive pulse into multiple impulses and equal drive pulses, the three-phase active APFC can effectively increase the drive frequency without increasing any hardware cost, thereby greatly reducing the volume and weight of the APFC.

[0007] In order to achieve the above object, the technical solution provided by the present invention is:

[0008] The present invention proposes a three-phase active APFC high-frequency control method based on the impulse equivalent principle, and the steps are as follows:

[0009] Step 1: Obtain the real-time frequency f, phase φ and amplitude of the grid voltage;

[0010] Step 2: Obtain the three-phase input current, and transform the three-phase ABC stationary coordinate system to the two-phase DQ rotating coordinate system to extract the active current Ip and reactive current Iq information;

[0011] Step 3: Obtain output voltage information Vdc;

[0012] Step 4: Perform closed-loop feedback control on the active current Ip, reactive current Iq and output voltage Vdc information obtained in step 2 and step 3 in the DQ coordinate system, and introduce the grid voltage information obtained in step 1 into the control loop as a feedforward signal, and obtain the three-phase AC modulation signal information: Sina, Sinb and Sinc by inverse dq / abc transformation of the command signal in the DQ coordinate system;

[0013] Step 5: According to the required switching frequency, the Sina, Sinb and Sinc signals calculated in step 8 are multiplied by the proportional coefficient K (K≤1) to obtain the three-phase AC modulation signals KSina, KSinb and KSinc, and the program calculation period Tc in step 2 is multiplied by the proportional coefficient K as the carrier period KTc;

[0014] Step 6: Compare and calculate the three-phase AC signals KSin, KSinb, KSinc obtained in step 5 with the carrier to generate a driving pulse width to drive the three-phase active APFC main switch tube.

[0015] Furthermore, the proportionality coefficient in step 5 is specifically described as follows:

[0016] 1. When K=1, the carrier cycle and the program calculation cycle are synchronized, and the program calculation cycle is the switching cycle;

[0017] 2. When K < 1, the three-phase AC modulation signal attenuates, the carrier period attenuates in the same proportion, and the switching frequency increases;

[0018] 3. When K=1, the pulse impulse σ1 generated by Sina, Sinb, Sinc and carrier Tc in step 4 is equal to the pulse impulse σ2 generated in step 6;

[0019] 4. When K is less than 1, the impulse σ2 of a single pulse in step six is ​​less than the impulse σ1 of a single pulse in step four. According to the impulse equivalence principle, by reasonably setting the Tc value and the K value, the equation σ1=K×σ2 can be satisfied within the Tc time period, that is, the impulse of a single pulse within Tc is equal to the sum of the impulses of K pulses.

[0020] In summary, by adopting the control method proposed in the present invention, the energy transmission of the three-phase active APFC can be guaranteed to remain unchanged while the switching frequency is increased, that is, high-frequency control of the three-phase active APFC can be achieved.

[0021] Furthermore, in step six, a regular sampling method is used to quickly compare and calculate the three-phase upper and lower complementary driving pulse width signals Sa, Sb and Sc, thereby realizing equivalent high-frequency switch driving based on the impulse equivalent principle.

[0022] Beneficial effects:

[0023] Compared with the prior art, the technical solution provided by the present invention has the following significant effects:

[0024] (1) The three-phase active APFC high-frequency control method based on the impulse equivalent principle proposed in the present invention effectively improves the driving frequency without increasing the hardware cost, greatly reduces the inductance of the input PFC inductor, reduces the overall volume and weight of the power supply, and greatly improves the power density of the power supply. It is particularly suitable for military fields with strict requirements on volume and weight.

[0025] (2) The three-phase active APFC high-frequency control method based on the impulse equivalent principle proposed in the present invention is easy to modify the switching frequency according to the actual needs of the project, realizes the flexibility of the control algorithm, facilitates the debugging and development of the power supply system, and shortens the project cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations of the present invention. In the accompanying drawings:

[0027] Figure 1 Schematic diagram of the topological structure of the three-phase active APFC in the present invention;

[0028] Figure 2 The coordinate diagram for the transformation from the three-phase stationary coordinate system to the two-phase rotating coordinate system is

[0029] Figure 3 The three-phase grid voltage phase-locked loop control principle block diagram used in this implementation example

[0030] Figure 4 This is the APFC control block diagram based on the pulse equivalent principle proposed by the present invention;

[0031] Figure 5 This is a schematic diagram of the work based on the pulse equivalent principle proposed by the present invention;

[0032] Figure 6 This is a flow chart of the control method proposed by the present invention. DETAILED DESCRIPTION

[0033] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings and examples.

[0034] The present invention proposes a three-phase active APFC high-frequency control method based on the impulse equivalent principle. Figure 1 The three-phase active APFC power supply system described in the present invention includes: a three-phase PFC inductor 1, a MOSFET three-phase rectifier bridge 2, a DSP core system and a control drive circuit 3, an inrush current suppression unit 4 and an output capacitor 5; the MOSFET three-phase rectifier bridge 2 is connected to the power grid through the three-phase PFC inductor 1; the output positive end of the MOSFET three-phase rectifier bridge 2 is connected to the positive end of the output capacitor 5; the output negative end of the MOSFET three-phase rectifier bridge 2 and the negative end of the output capacitor 5 are connected in series through the inrush current suppression unit to form a loop; the series circuit of the three-phase PFC inductor 1 contains an AC current sampling circuit, the two ends of the output capacitor 5 contain a DC voltage sampling circuit, and the series circuit of the inrush current suppression unit 4 contains a DC current sampling circuit; the sensor signal is connected to the DSP core system and the control circuit 3, and the PWM signal is generated by calculation to drive the MOSFET three-phase rectifier bridge 2.

[0035] The present invention proposes a three-phase active APFC high-frequency control method based on the impulse equivalent principle, which is a new control method invented by the inventor in the study of modular APFC technology. The inventor pointed out that the calculation of the three-phase active APFC is relatively complicated. Under the computing power of the existing digital control chip, it is difficult to effectively increase the switching frequency of the three-phase active APFC. In some applications with strict requirements on volume and weight, the commonly used switching frequency range cannot reduce the volume and weight of the APFC power supply system. Therefore, the inventor combines theoretical knowledge and practical experience, and innovatively applies the PWM generation mechanism, namely the impulse equivalent principle, to a single PWM pulse cycle, effectively realizing the replacement of the original single drive with an impulse area and multiple equal drive pulses, and completing the high-frequency control of the three-phase active APFC without increasing any hardware cost and space.

[0036] The implementation process of a three-phase active APFC high-frequency control method based on the impulse equivalent principle proposed by the present invention is specifically described below:

[0037] Step 1: Obtain real-time frequency f, phase φ and amplitude information of the grid voltage;

[0038] In steady state, Figure 1 The surge current suppression unit 4 is in a normally closed state. The three-phase grid voltage is sent to the DSP core system and the control drive circuit 3 through the AC voltage sampling circuit. The three-phase grid voltage Ua, Ub, and Uc are transformed by abc / dq. Please refer to the conversion diagram of the three-phase stationary coordinate system to the two-phase rotating coordinate system. Figure 2 , the transformation matrix is ​​shown in formula 1:

[0039] Formula 1

[0040] The SPLL algorithm is completed in the dq coordinate system to obtain the frequency f, phase φ and amplitude information of the grid voltage. Figure 3 This is the phase-locked control block diagram implemented in this example.

[0041] Step 2: Obtain the three-phase input current, and transform the three-phase ABC stationary coordinate system to the two-phase DQ rotating coordinate system to extract the active current Ip and reactive current Iq information;

[0042] The three-phase input current is sent to the DSP core system and the control drive circuit 3 through the AC current sampling circuit. According to the grid voltage phase obtained in step 1, the three-phase input current is transformed by abc / dq to obtain the active current Ip and reactive current Iq information in the DQ rotating coordinate system.

[0043] Step 3: Obtain output voltage information Vdc;

[0044] The output voltage information is sent to the DSP core system and the control drive circuit 3 through the DC voltage sampling circuit.

[0045] Step 4: Perform closed-loop feedback control on the active current Ip, reactive current Iq and output voltage Vdc information obtained in step 2 and step 3 in the DQ coordinate system, and introduce the grid voltage information obtained in step 1 into the control loop as a feedforward signal, and obtain the three-phase AC modulation signal information: Sina, Sinb and Sinc by inverse dq / abc transformation of the command signal in the DQ coordinate system;

[0046] The closed-loop feedback principle block diagram in this implementation case is as follows Figure 4 As shown, the three-phase input current is decoupled into active current component and reactive current component. The error adjustment output of the voltage outer loop is used as the given component of the active current of the current inner loop. The error adjustment output of the current inner loop is superimposed on the grid voltage feedforward signal and undergoes dq / abc transformation to obtain a three-phase AC modulation signal. The dq / abc transformation matrix is ​​shown in Formula 2:

[0047] Formula 2

[0048] After the above steps, a three-phase AC modulation signal can be obtained. In the existing known technical documents, this signal is used as a modulation signal and compared with a carrier to generate a PWM driving pulse.

[0049] Step 5: According to the required switching frequency, the Sina, Sinb and Sinc signals calculated in step 8 are multiplied by the proportional coefficient K (K≤1) to obtain the three-phase AC modulation signals KSina, KSinb and KSinc, and the program calculation period Tc in step 2 is multiplied by the proportional coefficient K as the carrier period KTc;

[0050] The PWM driving pulse generated by step 4, according to the required switching frequency, reduces the modulation signal and the carrier signal in the same proportion. The sum of the PWM pulse impulses generated within one period T is equal to the initial PWM pulse impulse. Please refer to Figure 5 As shown in the figure, taking K as 0.5 as an example, using the parallel line segmented proportionality theorem, it is easy to deduce that T2 is equal to T3, and the sum of T2 and T3 is equal to T1. According to the impulse equivalence principle, it can be concluded that within a period T, the impulse σ1 generated by the T1 drive pulse is equal to the sum of the impulse σ2 generated by the T2 drive and the impulse σ2 generated by the T3 drive. As mentioned above, it can be deduced that the energy transmitted by the T2 and T3 drive pulses within the period T is consistent with the energy transmitted by the T1 drive pulse, thereby realizing the high-frequency control of the three-phase active APFC.

[0051] The above analysis with K taken as 0.5 is only for the purpose of facilitating the understanding of the control scheme proposed by the present invention, and does not limit the protection scope of the present invention. Similarly, the high-frequency control scheme based on the impulse equivalence principle proposed by the scheme of the present invention is a new method for realizing high-frequency control without increasing hardware cost and space. This method is not only applicable to the scope of three-phase active APFC. As an ordinary designer of related professions, it is easy to apply the control scheme proposed by the present invention to other PWM converters without creative labor. All applications of the control method proposed by the present invention to realize high-frequency control of PWM converters should be regarded as the protection scope of the present invention.

[0052] Step 6: Compare and calculate the three-phase AC signals KSin, KSinb, KSinc obtained in step 5 with the carrier to generate a driving pulse width to drive the three-phase active APFC main switch tube;

[0053] In the DSP core system and control drive circuit 3, the three-phase modulation wave and the carrier are compared by the regular sampling method to generate a three-phase PWM drive, which is then isolated and amplified by the drive circuit to drive the three-phase active APFC main switch tube to achieve the power conversion function. Please refer to the working diagram of steps 1 to 6. Figure 6 , Figure 6 Shown is a schematic diagram of the control process in this implementation example.

Claims

1. A three-phase active APFC high-frequency control method based on the impulse equivalent principle, characterized in that The following steps are involved: Step 1: Obtain the real-time frequency f, phase Φ and amplitude of the grid voltage; Step 2: Obtain the three-phase input current, and transform the three-phase ABC stationary coordinate system to the two-phase DQ rotating coordinate system to extract the active current Ip and reactive current Iq information; Step three, obtain output voltage information Vdc; Step 4: Perform closed-loop feedback control on the active current Ip, reactive current lq and output voltage Vdc information obtained in step 2 and step 3 in the DQ coordinate system, and introduce the grid voltage information obtained in step 1 into the control loop as a feedforward signal, and obtain the three-phase AC modulation signal information: Sina, Sinb and Sinc by inverse dq / abc transformation of the command signal in the DQ coordinate system; The three-phase input current is decoupled into active current component and reactive current component. The error adjustment output of the voltage outer loop is used as the given component of the active current of the current inner loop. The error adjustment output of the current inner loop is superimposed on the grid voltage feedforward signal and subjected to dq / abc transformation to obtain a three-phase AC modulation signal. The dq / abc transformation matrix is ​​shown in Formula 2: Formula 2: After the above steps, the three-phase AC modulation signal can be obtained; Step 5: According to the required switching frequency, the Sina, Sinb and Sinc signals calculated in step 4 are multiplied by the proportional coefficient K, K≤1, to obtain the three-phase AC modulation signals KSina, KSinb and KSinc, and the program calculation period Tc is multiplied by the proportional coefficient K as the carrier period KTc; Step 6: Compare and calculate the three-phase AC signals KSin, KSinb, KSinc obtained in step 5 with the carrier cycle KTc to generate a driving pulse width for driving the three-phase active APFC main switch tube.

2. A three-phase active APFC high-frequency control method based on impulse equivalent principle according to claim 1, characterized in that: In the step 1, the three-phase grid voltage is sampled to perform abc / dq conversion, and the grid voltage amplitude, frequency and phase information are obtained through the SPLL algorithm.

3. A three-phase active APFC high-frequency control method based on impulse equivalent principle according to claim 1, characterized in that The closed-loop feedback control adopted in step 4 includes: In the step three, the output voltage is sampled and an error adjustment is performed with the given value. The error adjustment result is used as a reference signal for the active component of the current loop. Direct current control is performed in the DQ coordinate system, and a grid voltage feedforward signal is introduced. The command information in the DQ rotating coordinate system is transformed by dq / abc to obtain a three-phase AC modulation signal.

4. A three-phase active APFC high-frequency control method based on impulse equivalent principle according to claim 1, characterized in that In the step 5, the proportional coefficient K is not greater than 1, and the value of K is determined according to the actual required switching frequency.

5. The three-phase active APFC high-frequency control method based on the impulse equivalent principle according to claim 1 is characterized in that In the step six, the three-phase PWM drive pulse width is calculated using a regular sampling method.

6. A three-phase active APFC high-frequency control method based on impulse equivalent principle according to claim 4, characterized in that The influence of K value on switching frequency: (1) When K = 1, the carrier cycle and the program calculation cycle are synchronized, and the program calculation cycle is the switching cycle; (2) When K < 1, the three-phase AC modulation signal attenuates, the carrier period attenuates in the same proportion, and the switching frequency increases; (3) When K=1, the pulse impulse generated by Sina, Sinb, Sinc and carrier Tc 1 and the pulse impulse generated in step 6 of claim 1 2 equal; (4) When K < 1, the single pulse impulse generated in step 6 of claim 1 2 is less than the single pulse impulse in step 4 1. According to the impulse equivalent principle, by reasonably setting the Tc value and K value, the equation can be satisfied within the Tc time period. 1=K× 2, that is, the impulse of a single pulse within Tc is equal to the sum of the impulses of K pulses.

Images