A digital control method for step-down power factor correction in three-phase circuit

Abstract

The invention discloses a three-phase circuit step-down power factor correction digital control method, which belongs to the technical field of circuit control, and specifically comprises: after the three-phase alternating current is connected to a power supply, it is subjected to EMI filtering for interference suppression, and one path of the three-phase alternating current is input into a double-BUCK conversion circuit after passing through a rectifier bridge, and the double-BUCK conversion circuit comprises a power factor correction circuit and a DC / DC conversion circuit; after the three-phase alternating current is output from the double-BUCK conversion circuit, it is subjected to an output filtering circuit to reduce ripples, and then an input voltage sampling circuit is used to generate a voltage sampling signal, and the voltage sampling signal is input into a DSP control circuit to judge whether the input voltage is a voltage; when an input voltage abnormality signal is generated, the power factor correction circuit and the DC / DC conversion circuit are controlled to work at the same time; and a soft start circuit in the power supply is controlled to gradually increase the voltage on the high-voltage side capacitor to a preset voltage; the power factor correction circuit of the invention realizes the reduction of the reactive power loss of the circuit.

Description

Technical Field

[0001] The invention relates to the technical field of circuit control, and in particular to a three-phase circuit buck-type power factor correction digital control method. Background Art

[0002] The power factor defines the proportion of active power to apparent power. The greater the harmonic content in the current, the lower the power factor. The use of active power factor correction technology in the circuit can make the input current waveform close to a sine wave and in phase with the input voltage, thereby achieving the purpose of power factor correction. There are only three basic structures of power factor correction circuits, and all structures are based on the corresponding changes of these three basic structures. These three structures are: buck, boost, and buck-boost. Compared with the other two types of converters, the buck converter has its irreplaceable advantages, but due to the inherent cross-over distortion (Cross-overDistortion) of its input current, also known as the input current dead zone, its power factor can never reach the level that meets the requirements of various industrial standards, thus limiting the application of this structure in practice.

[0003] The three-phase power factor correction circuit has been widely used in medium and high power applications as the front-end power supply interfaced with the power grid; there are two mainstream solutions for the commonly used three-phase power factor correction circuit: the boost type three-phase PFC circuit and the buck type three-phase PFC circuit. Compared with the boost type circuit, the BCuk type solution has a wide output voltage range, no startup impact current and output current limiting capability, and has obvious advantages in specific applications.

[0004] However, when the circuit input is a three-phase AC voltage, the phase of the input voltage of each phase needs to be considered during control, and different control strategies are adopted for each switch tube with different phases; if an analog controller is used, the control logic is extremely complex, and both the current integral control method and the PWM control method have current distortion at the zero crossing point and the commutation point; at the same time, limited by the internal configuration of the existing digital control chip, the algorithm needs to occupy a large amount of digital core resources to achieve commutation, which affects many technical indicators of the main power circuit, objectively affecting the performance of the solution to a certain extent, and limiting the wider promotion and application of the solution. Summary of the invention

[0005] The purpose of the present invention is to provide a three-phase circuit buck power factor correction digital control method to solve the following technical problems:

[0006] When the circuit input is a three-phase AC voltage, the phase of the input voltage of each phase needs to be considered during control, and different control strategies should be adopted for each switch tube with different phases. If an analog controller is used, the control logic is extremely complex. At the same time, due to the internal configuration of the existing digital control chip, the algorithm needs to occupy a large amount of digital core resources to implement phase switching.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A three-phase circuit buck power factor correction digital control method is based on power supply, EMI filtering, rectifier bridge, dual-BUCK conversion circuit, output filtering circuit, odd harmonic injection circuit, input voltage sampling circuit, 9-way independent output auxiliary source, drive circuit, DSP control circuit, voltage sampling circuit, current sampling circuit, CAN communication circuit, including the following steps:

[0009] After the three-phase AC power is connected to the power supply and passes through the EMI filter for interference suppression, one path of the three-phase AC power is input into the dual-BUCK conversion circuit after passing through the rectifier bridge, and the other path is input into the 9-way independent output auxiliary source;

[0010] The dual-BUCK conversion circuit includes a power factor correction circuit and a DC / DC conversion circuit, and outputs 360V direct current; after the three-phase alternating current is output from the dual-BUCK conversion circuit, it passes through an output filter circuit to reduce ripples, and then is input into a voltage sampling circuit to generate a voltage sampling signal, which is input into a DSP control circuit to determine whether the input voltage has a phase loss, overvoltage, or undervoltage, and to generate an input voltage normal signal or a voltage abnormality signal;

[0011] When an input voltage abnormality signal is generated, the power factor correction circuit and the DC / DC conversion circuit are controlled to work at the same time; and the soft start circuit in the power supply is controlled to gradually increase the voltage on the high-voltage side capacitor to a preset voltage.

[0012] As a further solution of the present invention: three bidirectional switches Sy1, Sy2, and Sy3 are arranged between the midpoint of the dual-BUCK conversion circuit and the three-phase AC power input, and each of the bidirectional switches corresponds to each phase input in the three-phase AC power in sequence, forming an active harmonic injection circuit. When the input phase voltage value of any phase is not the maximum positive value or the minimum negative value, the diode corresponding to the bidirectional switch is not turned on, the input current is cut off, and the corresponding bidirectional switch Sy is constantly turned on to provide a freewheeling path, thereby increasing the conduction angle and improving the power factor.

[0013] As a further solution of the present invention: a resonant inductor Lr is introduced into the primary circuit of the power supply, and clamping diodes D1 and D2 are added to the primary of the power transformer.

[0014] As a further solution of the present invention: the dual-BUCK conversion circuit includes three bridge arms, each bridge arm is composed of a bidirectional switch and a parallel diode, and the on and off of the bidirectional switch is controlled by a PWM signal to control the flow direction of each phase current. When the voltage of any phase is positive, the forward switch in the corresponding bidirectional switch is turned on, and the current I on the corresponding inductor passing through the phase increases, and the inductor is charged, then the forward switch is turned off, and the current flows to the output end through the diode in parallel with the reverse switch, and the current I decreases; when the voltage of any phase is negative, the forward switch is turned on and the reverse switch is turned off.

[0015] As a further solution of the present invention: the on and off of the bidirectional switch is controlled by a PWM signal, and the PWM signal is adjusted by a triangle wave comparison method, a hysteresis control, and a space vector modulation method. The phase with the largest absolute voltage value among the three phases is not controlled, and only the other two phases are controlled.

[0016] As a further solution of the present invention: a fast recovery diode is connected in series on the DC side of each bridge arm circuit.

[0017] As a further solution of the present invention: the dual-BUCK conversion circuit is composed of two capacitors C1 and C2 connected in series for voltage division, the potential 0 at the midpoint of the capacitor is determined by the charging and discharging of the capacitor, the positive bus and the negative bus are sampled respectively, the difference is obtained and marked as a DC component, the DC component is superimposed on the input current reference sine wave after being adjusted by the compensator of the bias loop, and after precision rectification, it is converted into a double half-wave with different amplitudes as a given of the current loop.

[0018] As a further solution of the present invention: the control of the capacitor includes a phase-locked loop algorithm, PWM control and midpoint balance control.

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention comprehensively adopts EMI filter, active harmonic injection technology, advanced topological structure of bidirectional switch control, precise PWM modulation means and DSP real-time monitoring and control, which effectively improves the power factor, optimizes the power quality, enhances the system stability and reliability, and improves the system efficiency and the protection of circuit components. In addition, by introducing strategies such as resonant inductor Lr, fast recovery diode and capacitor midpoint balance control, the energy consumption is further reduced, ensuring efficient, stable and accurate power conversion control; under the condition of three-phase three-wire 380V AC input, the harmonic current of each phase is less than 3%, the power factor value is close to 1, and the power factor correction effect is excellent, which provides an efficient and reliable solution for the application field of power electronics;

[0021] (2) The power factor correction circuit of the present invention makes the input current follow the input voltage change, with a small phase shift and less reactive power generated, thereby reducing the load on the power grid, thereby saving costs and reducing reactive power losses. Secondly, since the input current has little distortion and is approximately sinusoidal, the harmonic current in the power grid is small, thereby reducing harmonic interference to other equipment and reducing the problem of neutral line heating caused by large harmonic currents. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] Figure 1 It is a schematic diagram of a module of the present invention;

[0024] Figure 2 is a circuit schematic diagram of the present invention;

[0025] Figure 3 1 is a circuit diagram of a soft start circuit of the present invention;

[0026] Figure 4 It is a circuit diagram of the dual-BUCK conversion circuit of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] See also Figure 1-4 As shown, the present invention is a three-phase circuit buck power factor correction digital control method, based on power supply, EMI filtering, rectifier bridge, dual BUCK conversion circuit, output filtering circuit, odd harmonic injection circuit, input voltage sampling circuit, 9 independent output auxiliary sources, drive circuit, DSP control circuit, voltage sampling circuit, current sampling circuit, CAN communication circuit, including the following steps:

[0029] After the three-phase AC power is connected to the power supply and passes through the EMI filter for interference suppression, one path of the three-phase AC power is input into the dual-BUCK conversion circuit after passing through the rectifier bridge, and the other path is input into the 9-way independent output auxiliary source;

[0030] The dual-BUCK conversion circuit includes a power factor correction circuit and a DC / DC conversion circuit, and outputs 360V direct current; after the three-phase alternating current is output from the dual-BUCK conversion circuit, it passes through an output filter circuit to reduce ripples, and then is input into a voltage sampling circuit to generate a voltage sampling signal, which is input into a DSP control circuit to determine whether the input voltage has a phase loss, overvoltage, or undervoltage, and to generate an input voltage normal signal or a voltage abnormality signal;

[0031] When an input voltage abnormality signal is generated, the power factor correction circuit and the DC / DC conversion circuit are controlled to work at the same time; and the soft start circuit in the power supply is controlled to gradually increase the voltage on the high-voltage side capacitor, thereby achieving the purpose of suppressing the input surge current.

[0032] In another preferred embodiment of the present invention, an advanced three-phase decoupled BUCK type PFC circuit is used. Buck is a step-down topology, avoiding multi-level and requiring no capacitor voltage grading ring. The main circuit schematic diagram is shown in FIG. Figure 3 . Three bidirectional switches Sy1, Sy2, and Sy3 are added between the midpoint of the two BUCKs and the three-phase input to form an active harmonic injection circuit. For each phase, when the input phase voltage value is in the middle (not the most positive or the most negative), the corresponding diode is not conducting and the input current is cut off. By controlling the corresponding bidirectional switch Sy to be constantly conducting during this period of time to provide a freewheeling path, the conduction angle is increased and the PF value is improved. The input power factor reaches 0.99, the harmonic current distortion is less than 5%, and the small total input harmonic current enables the module to meet the EMC and CE101 test requirements.

[0033] In another preferred embodiment of the present invention, the power supply adopts ZVSDC / DC conversion technology with clamping diodes, and the circuit schematic diagram is as follows: Figure 3 As shown in the figure, in order to realize ZVS soft switching, the primary circuit introduces a resonant inductor Lr. Due to the reverse recovery characteristics of the secondary rectifier diode, the instantaneous current in the resonant inductor Lr is greater than the current in the output inductor. When the secondary rectifier is cut off, voltage spikes and oscillations are generated at both ends of the rectifier, causing overvoltage and electromagnetic compatibility problems of the rectifier. Adding RC absorption at both ends of the secondary rectifier will increase the loss, and adding active clamping will reduce the reliability. To solve this problem, clamping diodes D1 and D2 are added to the primary of the transformer to feed back the excess energy in the resonant inductor to the primary power supply. The circuit is simple, the loss is reduced, and the efficiency and reliability are improved.

[0034] In another preferred embodiment of the present invention, the dual-BUCK conversion circuit includes three bridge arms, each bridge arm is composed of a bidirectional switch and a parallel diode, and the bidirectional switch is turned on and off by a PWM signal to control the flow direction of each phase current. When the voltage of any phase is positive, the forward switch in the corresponding bidirectional switch is turned on, and the current I on the corresponding inductor passing through the phase increases, and the inductor is charged, then the forward switch is turned off, and the current flows to the output end through the diode in parallel with the reverse switch, and the current I decreases; when the voltage of any phase is negative, the forward switch is turned on and the reverse switch is turned off. In practice, the control circuit is composed of a voltage outer loop, a current inner loop and a PWM generator.

[0035] In another preferred embodiment of the present invention, the on and off of the bidirectional switch is controlled by a PWM signal, and the PWM signal is adjusted by a triangle wave comparison method, a hysteresis control, and a space vector modulation method. The phase with the largest absolute voltage value among the three phases is not controlled, and only the other two phases are controlled; since the sum of the currents of the three phases is zero, it is sufficient to control the currents of only two of the phases. Therefore, in practical applications, the phase with the largest absolute voltage value is not controlled, and only the other two phases are selected for control. The advantage of this is that the number of switching actions is reduced, thereby reducing the total switching loss.

[0036] In another preferred embodiment of the present invention, a fast recovery diode is connected in series on the DC side of each bridge arm circuit.

[0037] The advantages of this circuit are low THD of input current, power factor of 1, low output DC voltage, high efficiency, bidirectional power transmission, and suitable for high-power applications. The disadvantages are that a large number of switches are used, the control is complex, the cost is high, and there is a risk of direct short circuit between the two series switches on each bridge arm, which requires high reliability of power drive control. In order to prevent the risk of direct short circuit, a fast recovery diode can be connected in series on the DC side of the circuit.

[0038] In another preferred embodiment of the present invention, the dual-BUCK conversion circuit is divided by two capacitors C1 and C2 in series, the potential 0 of the midpoint of the capacitor is determined by the charging and discharging of the capacitor, and the voltages of the two capacitors should be kept balanced to maintain a true three-level operating condition. Otherwise, the output voltage may contain undesirable harmonics and even affect the integrity of the circuit. The balance of the positive and negative busbars of the three-phase three-level PFC will affect the performance of the PFC;

[0039] The potential deviation of the capacitor midpoint is related to the charging and discharging process of the PFC positive and negative bus capacitors. The positive bus and negative bus are sampled separately, and then the difference (DC component) is obtained. The difference is adjusted by the compensator of the bias loop and superimposed on the input current reference sine wave. After precise rectification, it is transformed into a double half-wave with different amplitudes as the given current loop, so as to improve the PFC bus voltage balancing.

[0040] In another preferred embodiment of the present invention, the control of the capacitor includes a phase-locked loop algorithm, PWM control and mid-point balance control.

[0041] Phase-locked loop algorithm: It adopts advanced positive and negative sequence separated phase-locked algorithm, which can still work normally even if the line voltage is unbalanced within 15%, which is very excellent.

[0042] PWM control: adopts the most commonly used three-phase DQ conversion.

[0043] Midpoint balance control: This program uses hysteresis control method, which has high stability and small fluctuation, and can achieve a voltage difference within 5V.

[0044] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A three-phase circuit buck power factor correction digital control method, characterized in that: Based on power supply, EMI filtering, rectifier bridge, dual BUCK conversion circuit, output filtering circuit, odd harmonic injection circuit, input voltage sampling circuit, 9-way independent output auxiliary source, drive circuit, DSP control circuit, voltage sampling circuit, current sampling circuit, CAN communication circuit, the following steps are included: After the three-phase AC power is connected to the power supply and passes through the EMI filter for interference suppression, one path of the three-phase AC power is input into the dual-BUCK conversion circuit after passing through the rectifier bridge, and the other path is input into the 9-way independent output auxiliary source; The dual-BUCK conversion circuit includes a power factor correction circuit and a DC / DC conversion circuit, and outputs 360V direct current; after the three-phase alternating current is output from the dual-BUCK conversion circuit, it passes through an output filter circuit to reduce ripples, and then is input into a voltage sampling circuit to generate a voltage sampling signal, which is input into a DSP control circuit to determine whether the input voltage has a phase loss, overvoltage, or undervoltage, and to generate an input voltage normal signal or a voltage abnormality signal; When an input voltage abnormality signal is generated, the power factor correction circuit and the DC / DC conversion circuit are controlled to work at the same time; and the soft start circuit in the power supply is controlled to gradually increase the voltage on the high-voltage side capacitor to a preset voltage; Three bidirectional switches Sy1, Sy2, and Sy3 are arranged between the midpoint of the double-BUCK conversion circuit and the three-phase AC input. Each of the bidirectional switches corresponds to each phase input in the three-phase AC in sequence to form an active harmonic injection circuit. When the input phase voltage value of any phase is not the maximum positive value or the minimum negative value, the diode corresponding to the bidirectional switch is not turned on, the input current is cut off, and the corresponding bidirectional switch Sy is constantly turned on to provide a freewheeling path, thereby increasing the conduction angle and improving the power factor.

2. A three-phase circuit buck-type power factor correction digital control method according to claim 1, characterized in that: A resonant inductor Lr is introduced into the primary circuit of the power supply, and clamping diodes D1 and D2 are added to the primary of the power transformer.

3. A three-phase circuit buck power factor correction digital control method according to claim 1, characterized in that: The dual-BUCK conversion circuit includes three bridge arms, each of which is composed of a bidirectional switch and a parallel diode. The on and off of the bidirectional switch is controlled by a PWM signal to control the flow direction of each phase current. When the voltage of any phase is positive, the forward switch in the corresponding bidirectional switch is turned on, and the current I on the corresponding inductor passing through the phase increases, and the inductor is charged, then the forward switch is turned off, and the current flows to the output end through the diode in parallel with the reverse switch, and the current I decreases; when the voltage of any phase is negative, the forward switch is turned on and the reverse switch is turned off.

4. A three-phase circuit buck power factor correction digital control method according to claim 3, characterized in that: The on and off of the bidirectional switch is controlled by the PWM signal, and the PWM signal is adjusted by the triangle wave comparison method, hysteresis control, and space vector modulation method. The phase with the largest absolute value of the voltage among the three phases is not controlled, and only the other two phases are controlled.

5. A three-phase circuit buck power factor correction digital control method according to claim 1, characterized in that: A fast recovery diode is connected in series on the DC side of each bridge arm circuit.

6. A three-phase circuit buck power factor correction digital control method according to claim 1, characterized in that: The dual-BUCK conversion circuit is composed of two capacitors C1 and C2 connected in series for voltage division. The potential 0 at the midpoint of the capacitor is determined by the charging and discharging of the capacitor. The positive bus and the negative bus are sampled respectively, and the difference is obtained and marked as a DC component. The DC component is superimposed on the input current reference sine wave after being adjusted by the compensator of the bias loop, and is converted into a double half-wave with different amplitudes as a given of the current loop after precise rectification.

7. A three-phase circuit buck-type power factor correction digital control method according to claim 6, characterized in that: The control of the capacitor includes phase-locked loop algorithm, PWM control and mid-point balance control.

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