THD optimization method of single-phase single-stage AC / DC converter

Abstract

The invention discloses a THD optimization method of a single-phase single-stage AC / DC converter. The THD optimization method comprises the following steps: sampling an input voltage Vg of an AC side of an AC / DC conversion unit in the AC / DC converter; at the zero-crossing moment of the input voltage Vg, a low-frequency upper tube and a low-frequency lower tube of the AC / DC conversion unit are driven to switch the on-off state, and the on-off state comprises the on state and the off state; a control interval theta cri is set before and after the zero-crossing moment of the input voltage Vg, and PWM control is performed on a high-frequency upper tube and a high-frequency lower tube within the range of the control interval theta cri so as to restrain current distortion of the alternating current side; according to the invention, no extra hardware circuit is needed, the cost is effectively reduced, the PFC rectification function can be optimized, the input current distortion of the converter is effectively reduced, and the harmonic current injected into an AC power grid by the converter is reduced; the method can be applied to an OBC system of a new energy automobile so as to optimize the power density, the service life and the cost of the OBC.

Description

Technical Field

[0001] The invention relates to the technical field of power supply, and in particular to a THD optimization method for a single-phase single-stage AC / DC converter. Background Art

[0002] As a key component of electric vehicles, the on-board charger (OBC) converts external AC power into DC power to charge the electric vehicle battery. With the rapid development of the new energy vehicle industry, the installed capacity of OBC has increased sharply. On the one hand, a large number of AC / DC converters inject harmonic currents into the AC power grid, causing damage to the power quality of the power grid. On the other hand, the development of new energy vehicles has put forward higher requirements on the power density, cost and life of OBC.

[0003] Existing OBCs widely use an AC / DC converter cascaded DC-DC two-stage converter architecture, and the intermediate bus uses a large electrolytic capacitor for power decoupling. The AC / DC converter uses power factor correction (PFC) technology to improve the converter power factor (PF) and reduce the input current total harmonic distortion (THD). However, the two-stage converter architecture is not conducive to high power density, life and low cost of the system.

[0004] In order to achieve high power density, life and low cost optimization of OBC system, the single-phase single-stage AC / DC converter topology has attracted the attention of the industry and quickly became a research hotspot of OCB. The single-stage topology structure can realize the two-stage topology structure with a single-stage AC / DC converter, in which the AC / DC converter is used as the AC / DC unit and the DC-DC converter is used as the DC-DC unit. In addition, the primary switch tube of the DC-DC unit transformer of some topologies can be reused with the switch tube of the AC / DC unit, which not only saves the decoupling capacitor of the intermediate bus, but also saves some power devices, thereby greatly reducing the size and cost of the OBC and extending the service life of the OBC.

[0005] In order to realize the sinusoidalization of the input current of the single-phase single-stage AC / DC converter, a sinusoidal modulation strategy needs to be added to the circuit. However, the AC / DC converter contains an isolated DC-DC unit, and the duty cycle of the switch tubes of the AC / DC unit and the DC-DC unit needs to be coordinated to control. When the input voltage passes through zero, the duty cycle or shift ratio is close to 0, and the duty cycle of the converter is difficult to control accurately, which will cause the AC side current distortion and increase the AC current distortion rate. Therefore, the traditional single-phase single-stage AC / DC converter has the problem of poor input current THD, which needs to be optimized urgently. Summary of the invention

[0006] In order to solve the above defects in the prior art, the present invention proposes a THD optimization method for a single-phase single-stage AC / DC converter.

[0007] The technical solution adopted by the present invention is to design a THD optimization method for a single-phase single-stage AC / DC converter, sample the input voltage Vg of the AC / DC conversion unit on the AC side of the AC / DC converter; at the time when the input voltage Vg passes through zero, drive the low-frequency upper tube and the low-frequency lower tube of the AC / DC conversion unit to switch the switch state, and the switch state includes the on state and the off state; set a control interval θcri in the time period before and after the input voltage Vg passes through zero, and perform PWM control on the high-frequency upper tube and the high-frequency lower tube within the control interval θcri to suppress the current distortion on the AC side.

[0008] Preferably, performing PWM control on the high-frequency upper tube and the high-frequency lower tube within the control interval θcri specifically includes: determining the duty cycle of the high-frequency upper tube and the high-frequency lower tube according to the input voltage Vg, and setting the duty cycle of the high-frequency upper tube and the high-frequency lower tube within the control interval θcri according to D=1-|Vg / Vdc|, wherein Vdc is the output voltage of the AC / DC conversion unit.

[0009] Preferably, the THD optimization method further comprises: adjusting a phase shift angle φ of the inverter bridge of the DC / DC conversion unit in the AC / DC converter and the switch tube in the rectifier bridge following the input voltage angle θ of the input voltage Vg within the control interval θcri.

[0010] Preferably, the method for obtaining the phase shift angle φ specifically includes: obtaining an input voltage value V by a sampling circuit, a gain circuit and an ADC converter * g. Input current value I * g and the output voltage value V * 0; the input voltage value V * g is input into the phase-locked loop to obtain the input voltage angle θ, and then the input voltage angle θ is input into the input end of the phase follower; the output voltage value V0 is subtracted from the output voltage reference value V * o_ref is sent to controller 1 for control. The output of controller 1 is connected to the first limiter. The output value of the first limiter is multiplied by the output value of the phase follower to obtain the input current reference I * g_ref, and then the input current reference I * g_ref minus the input current value I * g is input to controller 1 for control, the output of the controller 2 is connected to the second limiter, and the second limiter outputs the phase shift angle φ.

[0011] Preferably, the optimization method also includes: within the control interval θcri, a high-frequency bridge arm PWM control signal is generated by comparing the duty cycle modulation signal Mi and the AC / DC conversion unit carrier signal Cq, and the duty cycle modulation signal Mi is a function of the input voltage angle θ representing the input voltage Vg; outside the control interval θcri, the positive and negative polarity of the input voltage Vg is determined according to a zero-crossing detection algorithm, and in the positive half-cycle of the input voltage Vg, one switch tube in the high-frequency bridge arm is controlled to remain turned on and the other switch tube is controlled to remain turned off, and in the negative half-cycle of the input voltage Vg, one switch tube in the high-frequency bridge arm is controlled to remain turned off and the other switch tube is controlled to remain turned on.

[0012] Optionally, determining the control interval θcri through the zero-crossing detection algorithm specifically includes: first detecting and obtaining the zero-crossing voltage Vb2 at the moment when the input voltage Vg crosses zero, adding the threshold voltage to the zero-crossing voltage Vb2 to generate an upper limit threshold voltage Vb1, recording the electrical angle corresponding to the upper limit threshold voltage Vb1 as the upper limit electrical angle θ1, subtracting the threshold voltage from the zero-crossing voltage Vb2 to generate a lower limit threshold voltage Vb3, recording the electrical angle corresponding to the lower limit threshold voltage Vb3 as the lower limit electrical angle θ3, and the interval corresponding to the upper limit threshold voltage Vb1 to the lower limit threshold voltage Vb3 is the control interval θcri.

[0013] Optionally, the THD optimization method also includes: maintaining a phase shift angle φ between the inverter bridge carrier signal Cp and the rectifier bridge carrier signal Cs; setting the inverter bridge duty cycle modulation signal equal to 0.5, and generating an inverter bridge PWM control signal after comparing the inverter bridge duty cycle modulation signal with the inverter bridge carrier signal Cp; setting the rectifier bridge duty cycle modulation signal equal to 0.5×f(θcri), where θcri is the control interval θcri, and f(θcri) is |sin(θ1)| within the control interval θcri, where θ1 is the upper limit electrical angle θ1, and f(θcri) is |sinθ| outside the control interval θcri, and generating a rectifier bridge PWM control signal after comparing the rectifier bridge duty cycle modulation signal with the rectifier bridge carrier signal Cs.

[0014] Optionally, the controller 1 adopts any one of a proportional P controller, a proportional integral PI controller and a 2P2Z controller; the controller 2 adopts any one of a proportional integral PI control, a PR control and a QPR controller.

[0015] Optionally, the bridge arms in the inverter bridge are reused, and the AC / DC conversion unit and the inverter bridge are integrated into a primary conversion unit, and the primary conversion unit adopts any one of a full-bridge conversion unit, a half-bridge conversion unit, or a conversion unit with a center-tapped transformer; when the primary conversion unit adopts a full-bridge conversion unit, the primary conversion unit includes a first bridge arm connected to the live wire of the input power supply through a first inductor L1, a second bridge arm connected to the live wire of the input power supply through a second inductor L2, and a third bridge arm connected to the neutral wire of the input power supply, wherein the first bridge arm and the second bridge arm are set as the high-frequency bridge arm, and the third bridge arm is set as the low-frequency bridge arm; when the primary conversion unit adopts In the case of a half-bridge type conversion unit, the primary conversion unit includes a first bridge arm connected to the live wire of the input power supply through a first inductor L1, and a second bridge arm connected to the neutral wire of the input power supply, the first bridge arm is set as the high-frequency bridge arm, and the second bridge arm is set as the low-frequency bridge arm; when the primary conversion unit adopts a conversion unit with a center-tapped transformer, the primary conversion unit includes a first bridge arm connected to the first winding N1 of the transformer through the first inductor L1, a second bridge arm connected to the second winding N2 of the transformer through the second inductor L2, and a third bridge arm connected to the input power supply, wherein the first bridge arm and the second bridge arm are set as the high-frequency bridge arm, and the third bridge arm is set as the low-frequency bridge arm.

[0016] The present invention also designs a single-phase single-stage AC / DC converter, which includes an AC / DC conversion unit, an inverter bridge, a high-frequency link transformer and a rectifier bridge connected in sequence; the converter adopts the THD optimization method of the single-phase single-stage AC / DC converter mentioned above.

[0017] The beneficial effects of the technical solution provided by the present invention are:

[0018] The present invention does not require additional hardware circuits, effectively reduces costs, can optimize PFC rectification functions, effectively reduce converter input current distortion, and reduce the harmonic current injected by the converter into the AC power grid; near the input voltage zero-crossing point, the control difficulty of the DC-DC unit is effectively reduced, the control robustness of the DC-DC unit is enhanced, and the control of the converter near the input voltage zero-crossing point is more reliable; it can work in continuous conduction mode (CCM), critical conduction mode (CRM) or discontinuous conduction mode (DCM), can broaden the modulation range of the converter, and is conducive to the design of single-phase single-stage AC / DC converters of different power levels; it is suitable for single-phase single-stage AC / DC converters based on magnetic integration technology and integrated three-ports, and is friendly to various single-phase single-stage AC / DC converter topologies; the inverter bridge and the bridge arm of the AC / DC unit are reused to further optimize the volume and cost of the single-phase single-stage AC / DC converter; it can be applied to the OBC system of new energy vehicles to optimize the OBC power density, life and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is described in detail below with reference to the embodiments and accompanying drawings, wherein:

[0020] Figure 1 It is the principle block diagram of a single-phase single-stage AC / DC converter;

[0021] Figure 2a It is a full-bridge single-phase single-stage AC / DC converter circuit diagram;

[0022] Figure 2b It is a circuit diagram of a half-bridge single-phase single-stage AC / DC converter;

[0023] Figure 2c It is a quasi-single-stage single-phase single-stage AC / DC converter circuit diagram;

[0024] Figure 2d It is a circuit diagram of a single-phase single-stage AC / DC converter with a center-tapped transformer;

[0025] Figure 3a It is the modulation strategy of single-phase single-stage AC / DC converter;

[0026] Figure 3b It is the modulation strategy of single-phase single-stage AC / DC converter;

[0027] Figure 4 It is a schematic diagram of the control principle of the single-phase single-stage AC / DC converter of the present invention;

[0028] Figure 5a It is the AC / DC unit output voltage simulation waveform;

[0029] Figure 5b It is a schematic diagram of the calculation principle of the control interval θcri range;

[0030] Figure 6a It is a schematic diagram of control waveforms for controlling the high-frequency bridge arm and the low-frequency bridge arm to improve the input current distortion rate of the present invention;

[0031] Figure 6b It is a comparison diagram of the control waveforms of each unit for optimizing the input current distortion rate of the present invention;

[0032] Figure 7a It is a comparison diagram of the simulated waveforms of the input voltage Vg and the input current Ig after the present invention optimizes the input current distortion rate;

[0033] Figure 7b This is a simulation waveform diagram of the primary voltage Vty after the present invention optimizes the input current distortion rate;

[0034] Figure 7c It is a simulation waveform diagram of the secondary voltage Vtf after the present invention optimizes the input current distortion rate;

[0035] Figure 8 It is a principle block diagram of a single-phase single-stage AC / DC converter with a resonant unit added to both the primary and secondary sides of the high-frequency link transformer;

[0036] Fig. 9 This is the principle block diagram of the THD optimization method. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] The present invention discloses a THD optimization method for a single-phase single-stage AC / DC converter. Figure 1 The converter principle block diagram shown in FIG. 1 includes an AC / DC conversion unit, an inverter bridge, a resonant unit A, a high-frequency link transformer and a rectifier bridge connected in sequence; see FIG. Fig. 9 The principle block diagram of the THD optimization method shown in the figure sets the switch tube in the AC / DC conversion unit as a high-frequency bridge arm and a low-frequency bridge arm, the high-frequency bridge arm includes a high-frequency upper tube and a high-frequency lower tube that are alternately turned on, and the low-frequency bridge arm includes a low-frequency upper tube and a low-frequency lower tube that are alternately turned on; the THD optimization method includes: S101. Sampling the input voltage Vg on the AC side of the AC / DC conversion unit in the AC / DC converter; S102. When the input voltage Vg passes through zero, driving the low-frequency upper tube and the low-frequency lower tube of the AC / DC conversion unit to switch the switch state, and the switch state includes a conducting state and a cut-off state; S103. Setting a control interval θcri in the time period before and after the input voltage Vg passes through zero, and performing PWM control on the high-frequency upper tube and the high-frequency lower tube within the control interval θcri to suppress the current distortion on the AC side.

[0039] It should be pointed out that the zero-crossing moment of the input voltage Vg refers to the moment when the AC voltage passes through zero voltage from positive to negative, or from negative to positive.

[0040] See also Figure 6aThe control waveform schematic diagram of the present invention for controlling the high-frequency bridge arm and the low-frequency bridge arm to improve the input current distortion rate is shown. The present invention divides the AC / DC conversion unit into a high-frequency tube and a low-frequency tube. The low-frequency slow tube performs on-off switching only when the positive and negative signs of the input voltage signal change. The high-frequency tube performs PWM control in the interval before and after the positive and negative signs change to control the energy input from the AC side, and at the same time increases the duty cycle or phase shift angle φ of the drive signal of the switch tube of the DC-DC conversion unit to a more appropriate size, thereby effectively solving the problem of input current distortion caused by the traditional AC / DC control method and generating a more perfect sinusoidal input current.

[0041] See also Figure 1 In the DC-DC unit, a resonant unit A is placed on the primary side of the high-frequency link transformer. The resonant unit A can be composed of different combinations of inductors, capacitors, and wires to form a common resonant circuit or DAB type circuit to achieve converter power transmission. The voltage at the Y1 terminal of the primary circuit is called the primary voltage Vty (see Figure 1 The Y1 terminal is both the output terminal of the inverter bridge and the port of the resonant cavity composed of the resonant unit A and the primary winding of the high-frequency link transformer). The voltage at the Y2 terminal of the secondary circuit is called the secondary voltage Vtf (see Figure 8 , the Y2 terminal is not only the input terminal of the rectifier bridge, but also the port of the resonant cavity composed of the resonant unit B and the secondary winding of the high-frequency link transformer). Figure 8 A resonance unit B is also provided on the secondary side of the high-frequency link transformer. The THD optimization method of the converter of this structure is the same as that of the present invention and will not be described in detail here.

[0042] In the prior art, the modulation strategy of a single-phase single-stage AC / DC converter is shown in FIG3. Figure 3a To determine the modulation method of the primary and secondary voltage phase shift, Figure 3b It is a modulation method that changes the phase shift of the primary and secondary voltages. Figure 3a It can be seen that within a switching cycle, the positive and negative voltage pulse widths of the primary voltage Vty and the secondary voltage Vtf are almost the same, the positive voltage pulse width of the primary voltage Vty is ΦyTs, and the positive voltage pulse width of the secondary voltage Vtf is ΦfTs. Φy is set to a constant value, Φf changes sinusoidally, and the transformation law is consistent with the absolute value of the input voltage; the phase shift angle between the primary voltage Vty and the secondary voltage Vtf is set to a constant value Φ3Ts, and the positive and negative signs of the phase shift angle Φ3Ts directly determine the direction of energy flow. Figure 3b It is a traditional phase shift modulation strategy. In one switching cycle, the positive and negative voltage pulse widths of the primary voltage Vty and the secondary voltage Vtf are almost the same. In the traditional modulation strategy, the positive voltage pulse widths of the primary voltage Vty and the secondary voltage Vtf are fixed values, and the phase shift angle between the two is obtained by calculation. This method results in a large reactive power in the circuit.

[0043] In the traditional modulation strategy, the low-frequency slow tube in the single-phase single-stage AC / DC converter will only be activated when the positive or negative sign of the input voltage signal changes, which makes the duty cycle or shift ratio of the high-frequency tube drive signal close to 0, which will cause the AC side current distortion. This patent adopts the method of activating the low-frequency slow tube near the zero point of the input voltage to control the energy input from the AC side and increase the duty cycle or shift ratio of the high-frequency tube drive signal to a more appropriate size.

[0044] In a preferred embodiment of the present invention, the PWM control of the high-frequency upper tube and the high-frequency lower tube within the control interval θcri specifically includes: determining the duty cycle of the high-frequency upper tube and the high-frequency lower tube according to the input voltage Vg, and setting the duty cycle of the high-frequency upper tube and the high-frequency lower tube within the control interval θcri according to D=1-|Vg / Vdc|, where Vdc is the output voltage of the AC / DC conversion unit.

[0045] In a preferred embodiment of the present invention, the THD optimization method further includes: adjusting the phase shift angle φ of the inverter bridge of the DC / DC conversion unit in the AC / DC converter and the switch tube in the rectifier bridge following the input voltage angle θ of the input voltage Vg within the control interval θcri.

[0046] Figure 2c It is a quasi-single-stage single-phase single-stage AC / DC converter circuit diagram. The present invention provides a control principle in combination with the circuit. Figure 4 Other variants of single-phase single-stage AC / DC converters can also be referenced Figure 4 The control principle is shown. Figure 4 The single-phase single-stage AC / DC converter AC / DC conversion unit shown includes: an AC side filter inductor L1, power switch tubes Q1, Q2, Q3, Q4, and a filter capacitor Cdc; a DC-DC unit includes power switch tubes Q5, Q6, Q7, Q8, a high-frequency isolation transformer, a leakage inductor Lp, power switch tubes Q9, Q10, Q11, Q12, and an output filter capacitor Co. The power switch tubes are all reverse-connected in parallel with a diode.

[0047] See also Figure 4 The control principle diagram of the single-phase single-stage AC / DC converter of the present invention is shown. The method for obtaining the phase shift angle φ specifically includes: sampling the input voltage Vg, the input current Ig on the AC side of the AC / DC conversion unit and the output voltage Vo of the rectifier bridge through the first sampling circuit and the first gain circuit K1, the second sampling circuit and the second gain circuit K2, the third sampling circuit and the third gain circuit K3 respectively, and then obtaining the input voltage value V through the ADC converter respectively. * g. Input current value I * g and the output voltage value V *o; the input voltage value V * g Input Phase Locked Loop ( Figure 4 The PLL in the circuit (English name: Phase-Locked Loop) obtains the input voltage angle θ, and then inputs the input voltage angle θ into the input end of the phase follower; the output voltage value Vo is subtracted from the output voltage reference value V * o_ref is sent to controller 1 for control. The output of controller 1 is connected to the first limiter. The output value of the first limiter is multiplied by the output value of the phase follower to obtain the input current reference I * g_ref, and then the input current reference I * g_ref minus the input current value I * g * The input controller 1 is controlled, and the output of the controller 2 is connected to the second limiter, and the second limiter outputs the phase shift angle φ. It should be pointed out that the function of the first limiter and the second limiter is to limit the size of the output value, which is equivalent to making the value output by the controller within the range set by this module. This module has a maximum value and a minimum value, and the output of the controller is between the maximum value and the minimum value.

[0048] It should be noted that: Figure 4 There are three ADC converters, the Chinese name is analog-to-digital converter, which are connected to the first gain circuit K1, the second gain circuit K2 and the third gain circuit K3 respectively to convert analog signals to digital signals. The phase follower can be expressed as a function of the input voltage angle θ of the input voltage Vg, with various forms such as sinθ, |sinθ|, |Vg| / Vm, and sinθ taking the absolute value, where Vm is the peak value of the input voltage Vg.

[0049] Combination Figure 4 and Figure 6a In the preferred embodiment shown, the optimization method further includes: determining the control interval θcri by a zero-crossing detection algorithm, generating a high-frequency bridge arm PWM control signal by comparing the duty cycle modulation signal Mi and the AC / DC conversion unit carrier signal Cq within the control interval θcri, wherein the duty cycle modulation signal Mi is a function of the input voltage angle θ representing the input voltage Vg; outside the control interval θcri, determining the positive and negative polarity of the input voltage Vg according to the zero-crossing detection algorithm, controlling one switch tube in the high-frequency bridge arm to remain on and the other switch tube to remain off during the positive half-cycle of the input voltage Vg, and controlling one switch tube in the high-frequency bridge arm to remain off and the other switch tube to remain on during the negative half-cycle of the input voltage Vg. It should be noted that the AC / DC conversion unit carrier signal Cq is a preset value.

[0050] Combination Figure 2c and Figure 4The embodiment shown is used for explanation, and the switch tubes Q1 and Q3 are set as high-frequency bridge arms, and the switch tubes Q2 and Q4 are set as low-frequency bridge arms. The control interval θcri is determined by the zero-crossing detection algorithm. Within the control interval θcri, the switch tubes Q1 and Q3 are controlled by the PWM signal generated by comparing the duty cycle modulation signal Mi with the AC / DC conversion unit carrier signal Cq, and the switch tubes Q2 and Q4 are controlled according to the positive half cycle and negative half cycle of the input voltage. Outside the control interval θcri, the switch tubes Q1, Q4 and Q2, Q3 are controlled according to the positive half cycle and negative half cycle of the input voltage. That is, within the control interval θcri, the switch tubes Q1 and Q3 are high-frequency, and the switch tubes Q2 and Q4 are low-frequency; outside the control interval θcri, the switch tubes Q1, Q4 and Q2, Q3 are all low-frequency. In the control interval θcri, due to the high frequency operation of the switch tubes Q1 and Q3, the energy input from the AC side can be controlled, so that the output voltage vpn of the AC / DC unit is raised within the control interval θcri, thereby changing the input voltage angle θ within the control interval θcri. The simulation waveform of the output voltage of the AC / DC unit is shown in Figure 5.

[0051] In an optional embodiment, determining the control interval θcri through a zero-crossing detection algorithm specifically includes: first detecting and obtaining the zero-crossing voltage Vb2 at the moment when the input voltage Vg crosses zero, adding the zero-crossing voltage Vb2 to the threshold voltage to generate an upper limit threshold voltage Vb1, recording the electrical angle corresponding to the upper limit threshold voltage Vb1 as the upper limit electrical angle θ1, subtracting the threshold voltage from the zero-crossing voltage Vb2 to generate a lower limit threshold voltage Vb3, recording the electrical angle corresponding to the lower limit threshold voltage Vb3 as the lower limit electrical angle θ3, and the upper limit electrical angle θ1 to the lower limit electrical angle θ3 corresponding to the interval between the upper limit threshold voltage Vb1 and the lower limit threshold voltage Vb3 is the control interval θcri.

[0052] See also Figure 4The schematic diagram of the control principle of the single-phase single-stage AC / DC converter of the present invention is shown. The THD optimization method also includes: setting the inverter bridge carrier signal Cp and the rectifier bridge carrier signal Cs, and maintaining a phase shift angle φ between the inverter bridge carrier signal Cp and the rectifier bridge carrier signal Cs; setting the inverter bridge duty cycle modulation signal equal to 0.5, and generating an inverter bridge PWM control signal after comparing the inverter bridge duty cycle modulation signal with the inverter bridge carrier signal Cp; setting the rectifier bridge duty cycle modulation signal equal to 0.5×f(θcri), where θcri is the control interval θcri, and within the control interval θcri, f(θcri) is |sin(θ1)|, where θ1 is the upper limit electrical angle θ1, and outside the control interval θcri, f(θcri) is |sinθ| (that is, within the control interval θcri, f(θcri) is the amplitude of |sinθ| at θ=θ1), and generating a rectifier bridge PWM control signal after comparing the rectifier bridge duty cycle modulation signal with the rectifier bridge carrier signal Cs.

[0053] Combination Figure 2c and Figure 4 The embodiment shown is used to illustrate that the second limiter outputs the phase shift angle φ, sets the inverter bridge carrier signal Cp and the rectifier bridge carrier signal Cs, and there is a phase shift angle φ between the inverter bridge carrier signal Cp and the rectifier bridge carrier signal Cs. The inverter bridge duty cycle modulation signal is set at a duty cycle of 0.5 and is compared with the inverter bridge carrier signal Cp to generate an inverter bridge PWM control signal, that is, Figure 2c and Figure 4 The PWM control signals of the switch tubes Q5, Q8, Q6, and Q7 are then obtained by the drive circuit 2. The duty cycle modulation signal of the rectifier bridge is equal to 0.5×f(θcri), and is compared with the rectifier bridge carrier signal Cs to generate the rectifier bridge PWM control signal, that is, Figure 2c and Figure 4 The PWM signals of the switch tubes Q9, Q12, Q10, Q11 are obtained, and then the drive circuit 3 obtains the drive signals of the switch tubes Q9, Q12, Q10, Q11.

[0054] In an optional embodiment, the controller 1 adopts any one of a proportional P controller, a proportional integral PI controller and a 2P2Z controller; the controller 2 adopts any one of a proportional integral PI control, a PR control and a QPR controller.

[0055] Combine the following Figure 2c and Figure 5bDetermining the control interval θcri is explained. Vb2 is the zero-crossing voltage Vb2 at the moment when the input voltage Vg crosses zero. The zero-crossing voltage Vb2 is added to the threshold voltage to generate the upper threshold voltage Vb1. The zero-crossing voltage Vb2 is subtracted from the threshold voltage to generate the lower threshold voltage Vb3. The digital values ​​of the threshold points corresponding to the upper threshold voltage Vb1, the zero-crossing voltage Vb2 and the lower threshold voltage Vb3 are converted by the ADC conversion relationship. Define flag 1, flag 2 and flag 3. When the input voltage Vg is equal to the threshold point C1 or the threshold point C3, flag 1 = 1, otherwise flag 1 = 0. When the input voltage Vg is greater than the upper threshold voltage Vb1, flag 2 = 1, and when the input voltage Vg is less than the lower threshold voltage Vb3, flag 2 = 0. When the input voltage Vg is equal to C4, flag 3 = 0. When the input voltage is equal to C2 and C3, flag 3 = 1, and flag 3 is used to determine the threshold point of the previous cycle. According to the status of flag 1, flag 2 and flag 3, the range of control interval θcri can be determined. Within the range of control interval θcri, switch tubes Q1 and Q3 operate at high frequency. When flag 2 is 1, it is the positive half cycle of input voltage, switch tube Q4 is turned on, and Q2 is turned off. When flag 2 is 0, it is the negative half cycle of input voltage, switch tube Q2 is turned on, and Q4 is turned off. Outside the range of control interval θcri, when flag 2 is 1, switch tubes Q1 and Q4 are turned on, and Q2 and Q3 are turned off. When flag 2 is 0, switch tubes Q1 and Q4 are turned off, and Q2 and Q3 are turned on.

[0056] See also Figure 6b The control waveform comparison diagram of each unit for optimizing the input current distortion rate of the present invention is shown. The control signals of the switch tubes Q5, Q8, Q6, and Q7 are obtained by setting the DC-DC unit switch tube to a duty cycle of 0.5. The control signals of the DC-DC unit switch tubes Q9, Q12, Q10, and Q11 are obtained by changing according to the f(θcri) law. In one switching cycle, the positive and negative voltage pulse widths of the primary voltage Vty and the secondary voltage Vtf are almost the same, and the conversion law is consistent with f(θcri). The phase shift angle φ between the primary voltage Vty and the secondary voltage Vtf is calculated by the control algorithm. The control interval θcri before and after the zero point of the input voltage Vg is obtained by calculation. Within the control interval θcri, the switch tubes Q1 and Q3 operate at high frequency, and outside the control interval θcri, they operate at low frequency according to the polarity of the input voltage. Figure 7a What is shown is a comparison diagram of the simulated waveforms of the input voltage Vg and the input current Ig after the input current distortion rate is optimized according to the present invention. Figure 7b The figure shows the simulation waveform of the primary voltage Vty after the present invention optimizes the input current distortion rate. The upper part of the figure is the simulation waveform of the primary voltage Vty in the interval of 0.12 seconds to 0.21 seconds, and the lower part of the figure is the simulation waveform of the primary voltage Vty in the interval of 0.16504 seconds to 0.1652 seconds; Figure 7bThe vertical coordinate is the voltage amplitude (in volts) and the horizontal coordinate is the time (in seconds). Figure 7c The figure shows a simulation waveform diagram of the secondary voltage Vtf after the present invention optimizes the input current distortion rate. The upper part of the figure is a simulation waveform diagram of the secondary voltage Vtf in the interval of 0.12 seconds to 0.21 seconds, and the lower part of the figure is a simulation waveform diagram of the secondary voltage Vtf in the interval of 0.16504 seconds to 0.1652 seconds; Figure 7c The vertical coordinate is the voltage amplitude (in volts), and the horizontal coordinate is the time (in seconds). Figure 7a , Figure 7b and Figure 7c It can be seen that after adopting the method for optimizing the input current distortion rate disclosed in the present invention, the input current is a sinusoidal current without distortion.

[0057] See also Figure 2c In one embodiment shown, the AC / DC conversion unit adopts a quasi-single-stage conversion unit, and the quasi-single-stage conversion unit includes a first bridge arm connected to the live line of the input power supply through a first inductor L1, and a second bridge arm connected to the neutral line of the input power supply, the first bridge arm is set as the high-frequency bridge arm, and the second bridge arm is set as the low-frequency bridge arm. Figure 2c In the illustrated embodiment, the first bridge arm includes a first switch tube Q1 and a third switch tube Q3 , and the second bridge arm includes a second switch tube Q2 and a fourth switch tube Q4 .

[0058] In an optional embodiment, the bridge arms in the inverter bridge are reused, and the AC / DC conversion unit and the inverter bridge are integrated into a primary conversion unit, and the primary conversion unit adopts any one of a full-bridge conversion unit, a half-bridge conversion unit or a conversion unit with a center-tapped transformer.

[0059] See also Figure 2a In one embodiment shown, when the primary conversion unit adopts a full-bridge conversion unit, the primary conversion unit includes a first bridge arm connected to the live wire of the input power supply through a first inductor L1, a second bridge arm connected to the live wire of the input power supply through a second inductor L2, and a third bridge arm connected to the neutral wire of the input power supply, wherein the first bridge arm and the second bridge arm are set as the high-frequency bridge arm, and the third bridge arm is set as the low-frequency bridge arm. Figure 2a In the illustrated embodiment, the first bridge arm includes a first switch tube Q1 and a third switch tube Q3 , the second bridge arm includes a second switch tube Q2 and a fourth switch tube Q4 , and the third bridge arm includes a fifth switch tube Q5 and a sixth switch tube Q6 .

[0060] See also Figure 2bIn one embodiment shown, when the primary conversion unit adopts a half-bridge conversion unit, the primary conversion unit includes a first bridge arm connected to the live line of the input power supply through a first inductor L1, and a second bridge arm connected to the neutral line of the input power supply, the first bridge arm is set as the high-frequency bridge arm, and the second bridge arm is set as the low-frequency bridge arm. Figure 2b In the illustrated embodiment, the first bridge arm includes a first switch tube Q1 and a third switch tube Q3 , and the second bridge arm includes a second switch tube Q2 and a fourth switch tube Q4 .

[0061] See also Figure 2d In one embodiment shown, when the primary conversion unit adopts a conversion unit with a center-tapped transformer, the primary conversion unit includes a first bridge arm connected to the first winding N1 of the transformer through a first inductor L1, a second bridge arm connected to the second winding N2 of the transformer through a second inductor L2, and a third bridge arm connected to an input power supply, wherein the first bridge arm and the second bridge arm are set as the high-frequency bridge arm, and the third bridge arm is set as the low-frequency bridge arm. Figure 2d In the illustrated embodiment, the first bridge arm includes a first switch tube Q1 and a third switch tube Q3 , the second bridge arm includes a second switch tube Q2 and a fourth switch tube Q4 , and the third bridge arm includes a fifth switch tube Q5 and a sixth switch tube Q6 .

[0062] The present invention also discloses a single-phase single-stage AC / DC converter, which includes an AC / DC conversion unit, an inverter bridge, a high-frequency link transformer and a rectifier bridge connected in sequence; the converter adopts the THD optimization method of the single-phase single-stage AC / DC converter mentioned above.

[0063] The above embodiments are for illustration only and are not intended to be limiting. Any equivalent modifications or changes made thereto without departing from the spirit and scope of the present application shall be included in the scope of the claims of the present application.

Claims

1. A THD optimization method for a single-phase single-stage AC / DC converter, characterized in that: include: Sampling an input voltage Vg of an AC side of an AC / DC conversion unit in the AC / DC converter; At the moment when the input voltage Vg passes through zero, driving the low-frequency upper tube and the low-frequency lower tube of the AC / DC conversion unit to switch the switch state, wherein the switch state includes an on state and an off state; A control interval θcri is set before and after the input voltage Vg passes through zero, and PWM control is performed on the high-frequency upper tube and the high-frequency lower tube within the control interval θcri to suppress the current distortion on the AC side.

2. The THD optimization method of a single-phase single-stage AC / DC converter according to claim 1, characterized in that: The PWM control of the high-frequency upper tube and the high-frequency lower tube within the control interval θcri specifically includes: determining the duty cycle of the high-frequency upper tube and the high-frequency lower tube according to the input voltage Vg, and setting the duty cycle of the high-frequency upper tube and the high-frequency lower tube within the control interval θcri according to D=1-|Vg / Vdc|, where Vdc is the output voltage of the AC / DC conversion unit.

3. The THD optimization method of a single-phase single-stage AC / DC converter according to claim 2, characterized in that: The THD optimization method further includes: adjusting a phase shift angle φ of switches in an inverter bridge and a rectifier bridge of a DC / DC conversion unit in the AC / DC converter in accordance with an input voltage angle θ of the input voltage Vg within the control interval θcri.

4. The THD optimization method of a single-phase single-stage AC / DC converter according to claim 3, characterized in that: The method for obtaining the phase shift angle φ specifically includes: obtaining an input voltage value V by a sampling circuit, a gain circuit and an ADC converter * g. Input current value I * g and the output voltage value V * o; the input voltage value V * g is input into the phase-locked loop to obtain the input voltage angle θ, and then the input voltage angle θ is input into the input end of the phase follower; the output voltage value Vo is subtracted from the output voltage reference value V * o_ref is sent to controller 1 for control. The output of controller 1 is connected to the first limiter. The output value of the first limiter is multiplied by the output value of the phase follower to obtain the input current reference I * g_ref, and then the input current reference I * g_ref minus the input current value I * g is input to controller 1 for control, the output of the controller 2 is connected to the second limiter, and the second limiter outputs the phase shift angle φ.

5. The THD optimization method of a single-phase single-stage AC / DC converter according to claim 4, characterized in that: The optimization method further comprises: Within the control interval θcri, a high-frequency bridge arm PWM control signal is generated by comparing the duty cycle modulation signal Mi and the AC / DC conversion unit carrier signal Cq, and the duty cycle modulation signal Mi is a function of the input voltage angle θ representing the input voltage Vg; outside the control interval θcri, the positive and negative polarities of the input voltage Vg are determined according to the zero-crossing detection algorithm, and in the positive half cycle of the input voltage Vg, one switch tube in the high-frequency bridge arm is controlled to remain turned on and the other switch tube is controlled to remain turned off, and in the negative half cycle of the input voltage Vg, one switch tube in the high-frequency bridge arm is controlled to remain turned off and the other switch tube is controlled to remain turned on.

6. The THD optimization method of a single-phase single-stage AC / DC converter according to claim 5, characterized in that: The method of determining the control interval θcri by the zero-crossing detection algorithm specifically includes: first detecting and obtaining the zero-crossing voltage Vb2 at the moment when the input voltage Vg crosses zero, adding the threshold voltage to the zero-crossing voltage Vb2 to generate the upper threshold voltage Vb1, recording the electrical angle corresponding to the upper threshold voltage Vb1 as the upper electrical angle θ1, subtracting the threshold voltage from the zero-crossing voltage Vb2 to generate the lower threshold voltage Vb3, recording the electrical angle corresponding to the lower threshold voltage Vb3 as the lower electrical angle θ3, and the interval corresponding to the upper threshold voltage Vb1 to the lower threshold voltage Vb3 is the control interval θcri.

7. The THD optimization method of a single-phase single-stage AC / DC converter according to claim 6, characterized in that: The THD optimization method further includes: maintaining a phase shift angle φ between the inverter bridge carrier signal Cp and the rectifier bridge carrier signal Cs; setting the inverter bridge duty cycle modulation signal equal to 0.5, and generating an inverter bridge PWM control signal after comparing the inverter bridge duty cycle modulation signal with the inverter bridge carrier signal Cp; Let the rectifier bridge duty cycle modulation signal be equal to 0.5×f(θcri), where θcri is the control interval θcri, and within the control interval θcri, f(θcri) is |sin(θ1)|, where θ1 is the upper limit electrical angle θ1, and outside the control interval θcri, f(θcri) is |sinθ|. The rectifier bridge duty cycle modulation signal is compared with the rectifier bridge carrier signal Cs to generate a rectifier bridge PWM control signal.

8. The THD optimization method of a single-phase single-stage AC / DC converter according to claim 4, characterized in that: The controller 1 adopts any one of a proportional P controller, a proportional integral PI controller and a 2P2Z controller; the controller 2 adopts any one of a proportional integral PI control, a PR control and a QPR controller.

9. The THD optimization method of a single-phase single-stage AC / DC converter according to any one of claims 1 to 8, characterized in that: The bridge arms in the inverter bridge are reused, and the AC / DC conversion unit and the inverter bridge are integrated into a primary conversion unit, wherein the primary conversion unit adopts any one of a full-bridge conversion unit, a half-bridge conversion unit, or a conversion unit with a center-tapped transformer; When the primary conversion unit adopts a full-bridge conversion unit, the primary conversion unit includes a first bridge arm connected to the live wire of the input power supply through a first inductor L1, a second bridge arm connected to the live wire of the input power supply through a second inductor L2, and a third bridge arm connected to the neutral wire of the input power supply, wherein the first bridge arm and the second bridge arm are set as the high-frequency bridge arm, and the third bridge arm is set as the low-frequency bridge arm; When the primary conversion unit adopts a half-bridge conversion unit, the primary conversion unit includes a first bridge arm connected to the live line of the input power supply through the first inductor L1, and a second bridge arm connected to the neutral line of the input power supply, the first bridge arm is set as the high-frequency bridge arm, and the second bridge arm is set as the low-frequency bridge arm; When the primary conversion unit adopts a conversion unit with a center-tapped transformer, the primary conversion unit includes a first bridge arm connected to the first winding N1 of the transformer through a first inductor L1, a second bridge arm connected to the second winding N2 of the transformer through a second inductor L2, and a third bridge arm connected to an input power supply, wherein the first bridge arm and the second bridge arm are set as the high-frequency bridge arm, and the third bridge arm is set as the low-frequency bridge arm.

10. A single-phase single-stage AC / DC converter, comprising an AC / DC conversion unit, an inverter bridge, a high-frequency link transformer and a rectifier bridge connected in sequence; characterized in that: The converter adopts the THD optimization method of the single-phase single-stage AC / DC converter according to any one of claims 1 to 9.

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