A method of controlling a combined ac / ac converter

Abstract

The application discloses a combined AC / AC converter control method, and relates to the technical field of power electronic converter control. The combined AC / AC converter is composed of a passive rectification bridge, a Boost converter and a DC / AC converter. The Boost converter is used for intermediate bus voltage control and AC input side power factor correction; the DC / AC converter dynamically divides a carrier area according to a passive rectification output voltage and an intermediate bus voltage amplitude, and dynamically adjusts a modulation wave amplitude in combination with an AC input and output voltage phase relationship, so that rectification output current limiting and non-circulating power control are realized while AC output voltage control is completed, and then active power optimization is realized. Based on the control method, the application can realize collaborative control of the Boost converter and the DC / AC converter, so that the combined AC / AC converter has the technical advantages of small power conversion stages and excellent power factor, and can effectively improve system conversion efficiency, reduce system cost, improve power supply quality and improve system operation reliability.

Description

Technical Field

[0001] This invention relates to a combined AC / AC converter control method, belonging to the field of power electronic converter control technology. Background Technology

[0002] Power conversion devices are the core carriers for achieving efficient conversion and interconnection of different forms of electrical energy. Among them, AC / AC converters are widely used in wind power generation, motor drive, uninterruptible power supply systems and microgrids.

[0003] Existing AC / AC converters are mainly divided into two topologies: single-stage and two-stage. Single-stage AC / AC converters, typically represented by matrix converters, effectively improve energy transfer efficiency and reduce system cost by eliminating one power conversion stage. However, this type of topology lacks an intermediate energy storage unit, resulting in high input-output voltage coupling and low voltage utilization, which limits its engineering application and large-scale deployment. Two-stage AC / AC converters, through an intermediate DC energy storage stage, can achieve flexible control of the amplitude, phase, and frequency of the input and output voltages, adapting to any AC input-output operating conditions. However, since all power must undergo rectification and inversion stages sequentially, there are inherent problems such as a large number of power conversion stages, high intermediate DC bus voltage, and high stress on power devices, which not only increases system cost but also restricts further improvement in energy transfer efficiency.

[0004] Patent (Publication No.: CN118100601A) proposes a quasi-single-stage DC / AC converter topology that combines the advantages of single-stage and two-stage converters. In this topology, most of the energy is directly transferred to the load side via a full-bridge inverter, reducing the proportion of power transferred from the DC input source to the load side through the Boost converter. This effectively reduces the number of power conversion stages and improves system conversion efficiency. The main circuit scheme provided by this patent can be further improved to realize a quasi-single-stage AC / AC converter. It only requires rectifying the AC input voltage to the power frequency to form a DC voltage with twice the grid pulsation frequency, which is then used as the input to the quasi-single-stage DC / AC converter. However, this improved combined AC / AC converter exhibits a pulsating characteristic at twice the grid frequency in the DC voltage output from the passive rectifier bridge, which is significantly different from traditional DC / AC converters that use a voltage-stable DC source as input. Therefore, the quasi-single-stage DC / AC control method proposed in the patent (publication number: CN118100601A) cannot be used to control combined AC / AC converters, and there is currently no readily available control method to solve the control problem of such combined AC / AC converters. Specific problems include: 1. In AC / AC conversion scenarios, the AC input voltage and AC output voltage are decoupled, and their frequency, amplitude, and phase relationship are arbitrary. When a phase difference exists, reactive circulating current will appear in the combined AC / AC converter system, significantly reducing the system's power factor, power quality, and efficiency; 2. In combined AC / AC converters, there is no large-capacity decoupling capacitor on the rectifier bridge output side, so coupling between the AC input and AC output is inevitable. The pulsating rectified output voltage will directly affect the waveform quality of the AC output voltage, reducing the system's output quality.

[0005] To address the aforementioned issues, this invention proposes a control method for efficient conversion and high-quality waveforms in combined AC / AC converters. This method enables coordinated control of the Boost converter and the DC / AC converter, reducing the number of equivalent power conversion stages, improving system efficiency, and lowering system costs, while simultaneously eliminating reactive circulating current, improving the system power factor, and enhancing power supply quality. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a combined AC / AC converter control method. The combined AC / AC converter is composed of a passive rectifier bridge, a boost converter, and a DC / AC converter. The boost converter is used for intermediate bus voltage control and AC input power factor correction. The DC / AC converter dynamically divides the carrier region based on the amplitude of the passive rectifier output voltage and the intermediate bus voltage, and dynamically adjusts the modulation amplitude based on the phase relationship between the AC input and output voltages. This achieves both AC output voltage control and rectifier output current limiting and circulating current-free power control, thereby optimizing active power. Based on the above control strategy, this invention enables coordinated control of the Boost converter and the DC / AC converter: First, it allows most of the power to be output directly from the input via the DC / AC converter, effectively reducing the number of power conversion stages while retaining the high-efficiency energy transfer advantage of a single-stage AC / AC converter; second, it reduces the rating and capacity of the Boost converter, lowering system costs; third, the Boost converter can achieve input-side power factor correction, and the DC / AC converter, by dynamically adjusting the modulation wave and carrier region, controls the AC output voltage and limits the rectified output current, achieving circulating current-free power control, thereby optimizing active power and effectively improving the power supply quality of the AC / AC converter; fourth, it achieves decoupling between AC input and output, improving the system's disturbance rejection capability. This gives the combined AC / AC converter the technical advantages of a small number of power conversion stages and a superior power factor, effectively improving system conversion efficiency, reducing system costs, improving power supply quality, and enhancing system operational reliability.

[0007] To achieve the above objectives, this invention employs a combined AC / AC converter. The combined AC / AC converter is composed of a passive rectifier bridge, a boost converter, and a DC / AC converter, wherein the DC / AC converter includes a switching transistor. S 1~ S 4. Switching transistor S d1 ~ S d4 Output inductor L o and output capacitor C o Switching transistor S 1. Drain connection to switching transistor S 3 drains, switching transistors S 2 source-connected switching transistors S 4 sources, switching transistors S d1 Source-connected switching transistor S d3 Source, switch S d1 Drain connection switching transistor Sd2 Drain, switching transistor S d3 Drain connection switching transistor S d4 Drain, switching transistor S d2 Source and switching transistor S 1. Source and switch transistor S 2. Drain and output inductors L o Connected on the left, output inductor L o The output capacitor is connected on the right side. C o Positive terminal, output capacitor C o Negative electrode and switching transistor S 3. Source and Switch S 4. Drain and switching transistor S d4 Source and pole connected;

[0008] The converter configuration is as follows: the AC source is connected to the input of the passive rectifier bridge, the positive output of the passive rectifier bridge is connected to the positive input of the Boost converter, and the switching transistor of the DC / AC converter. S d1 Source, switch S d3 The source terminals are connected, and the positive output terminal of the Boost converter is connected to the switching transistor of the DC / AC converter. S 1. Drain and switching transistor S The drains of the three passive rectifier bridges are connected together. The negative output of the passive rectifier bridge is connected to the negative output of the Boost converter and the DC / AC converter. The output of the DC / AC converter is connected to the load.

[0009] The specific control method for the combined AC / AC converter is as follows:

[0010] Boost converter controls intermediate bus voltage V H and inductor current i B This includes the following steps: real-time sampling of the intermediate bus voltage. V H The intermediate bus voltage reference V Href Subtract the intermediate bus voltage V H The error signal is obtained, and after processing by the PI controller, the effective value of the current loop reference signal is obtained. i R Sampled AC input voltage u ac And process it to obtain its absolute value | uac |, and the input phase signal coefficients K in Multiply the two, and the result of multiplying them is the same as the effective value of the current loop reference signal. i R Multiplication generates a current loop reference signal i Bref Input phase signal coefficients K in The calculation formula is as follows:

[0011] ;

[0012] in u ac_rms Sampled AC input voltage u ac The effective values ​​obtained after processing; i Bref Subtract inductor current i B With rectified output current i L The error signal is obtained, and this error signal is used to generate a control signal through a PI controller. d 0, control signal d 0 and control signal feedforward d feed The sums are then modulated by PWM and used as the drive signal for the switching transistor Q, thereby controlling the intermediate bus voltage. V H and inductor current i B The control, in which the control signal feedforward d feed The calculation formula is as follows:

[0013] ;

[0014] DC / AC converter controls AC output voltage v o and rectified output current i L The process includes the following steps: using stacked carriers with positive half-cycle amplitudes of 1 to 0 and negative half-cycle amplitudes of 0 to -1. v c Furthermore, the carrier frequencies for both positive and negative half-cycles are the same; the passive rectifier output voltage is sampled in real time. v L and intermediate bus voltage V H Multiply the carrier wave with a positive half-cycle amplitude of 1 to 0 by v L / V H Obtain carrierv pos_bot , 1- v pos_bot As a carrier v pos_top Therefore, two sets of carrier waves can be obtained during the positive half-cycle. v pos_bot and v pos_top Their dividing line is v L / V H ,use v c_pos This indicates that; similarly, the two sets of carriers in the negative half-cycle can be obtained. v neg_top and v neg_bot Their dividing line is - v L / V H ,use v c_neg This indicates that the superimposed carriers... v c Divided into four different carrier groups v pos_top , v pos_bot , v neg_top and v neg_bot Real-time sampling of AC output voltage v o AC output voltage reference v oref Subtract AC output voltage v o The error signal is obtained, and the obtained error signal is then passed through a PI controller to obtain a modulated wave. v r The modulated wave v r The amplitude ranges from -1 to 1; when the AC input voltage... u ac With AC output voltage v o When in phase or out of phase, the system has no circulating power, and the modulated wave... v r With carrier v pos_top Intercepting the drive signal generated by the switching transistor S1 d s1 Switch S d1 Complementary to switch S1; Modulated wave v r With carrier vpos_bot Intersection generation of switching transistor S d2 drive signal d sd2 Switch S2 and switch S d2 Complementary; Modulated wave v r With carrier v neg_top Generate switching transistor S d3 drive signal d sd3 Switch S3 and switch S d3 Complementary; Modulated wave v r With carrier v neg_bot Intercepting to generate the drive signal for switch S4 d s4 Switch S d4 Complementary to switch S4; when AC input voltage u ac With AC output voltage v o At any phase that is neither in-phase nor out-of-phase, and the AC input current i in Less than the rectified output current i L At this time, the system has reactive circulating power, and the original modulated wave v r Change to v r_new1 and v r_new2 Modulated wave v r_new1 and v r_new2 The driving signals for the switching transistors are generated by intersecting with different carrier waves, wherein the modulated wave... v r_new1 and v r_new2 Amplitude and power limiting factor K pL It can be obtained through the following calculations:

[0015] ;

[0016] Among them, the modulated wave v r_new1 and v r_new2 The amplitude is limited, with both ranging from -1 to 1. v omax This represents the maximum AC output voltage. v LmaxBoth are non-zero, representing the maximum output voltage of the passive rectifier; modulated wave. v r_new1 With carrier v pos_top carrier v neg_top Intersection, generating switching transistors S1 and S2 respectively. d3 drive signal d s1 and d sd3 Switch S d1 And switching transistor S3 is connected to switching transistor S1 and switching transistor S2 respectively. d3 Complementary, modulated wave v r_new2 With carrier v pos_bot carrier v neg_bot Intersection, generating switching transistor S respectively d2 and the drive signal of the switching transistor S4 d sd2 and d s4 Switch S2 and switch S d4 Respectively with switching transistor S d2 It is complementary to switch S4. Therefore, when there is no circulating power in the system, the converter modulation wave is only generated by... v r Decision; when circulating power exists in the system, the converter modulation wave is determined by... v r_new1 and v r_new2 Decide.

[0017] The present invention has the following beneficial technical effects:

[0018] (1) The topology of this invention is based on the industrially mature passive rectifier bridge, Boost converter and DC / AC converter, which improves performance while ensuring a simple system structure and high reliability.

[0019] (2) This invention achieves coordinated control of the Boost converter and the DC / AC converter through the topology design and control method of converter combination: most of the power is directly output from the input through the DC / AC converter, which effectively reduces the number of power conversion stages and retains the advantages of efficient energy transmission of the single-stage AC / AC converter; at the same time, it reduces the rating and capacity of the Boost converter and reduces the system cost; at the same time, the Boost converter can realize input-side power factor correction, and the DC / AC converter can control the AC output voltage and limit the rectified output current by dynamically adjusting the modulation wave and carrier region, thereby achieving non-circulating current power control, thus realizing active power optimization and effectively improving the power supply quality of the AC / AC converter; it also realizes decoupling between AC input and output and improves the reliability of system operation. Attached Figure Description

[0020] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the invention will be briefly described below:

[0021] Figure 1 This is a block diagram of the control strategy for a combined AC / AC converter.

[0022] Figure 2 For combined AC / AC converters with AC input voltage u ac With inverter output voltage v o The modulation principle diagram of the system having no reactive circulating current power when in phase or out of phase;

[0023] Figure 3 For combined AC / AC converters with AC input voltage u ac With inverter output voltage v o At any phase that is neither in-phase nor out-of-phase, and the AC input current i in Less than the rectified output current i L The modulation principle diagram when reactive circulating current power exists in the system;

[0024] Figure 4 The experimental waveform diagram of the combined AC / AC converter;

[0025] Figure 5 For efficiency comparison chart;

[0026] Figure 6 The power factor test results are for the AC input side of the combined AC / AC converter.

[0027] The labels in the above diagram are named as follows: u acAC input voltage; i in AC input current; i in_rms This is the effective value of the input current; i inref For AC input current reference; D z1 ~D z4 All are rectifier diodes; v L This is the output voltage of the passive rectifier; v Lmax This represents the maximum output voltage of the passive rectifier. i L The rectified output current flowing into the DC / AC converter from the passive rectifier bridge; L B For energy storage inductors; i B The inductor current flowing through the energy storage inductor; i Bref This is the reference signal for the current loop of the Boost converter; C H For filtering capacitors; V H This refers to the intermediate bus voltage. V Href This is the reference for the intermediate bus voltage; Q is the switching transistor, and D is the freewheeling diode; L o and C o These are the output inductor and the output capacitor, respectively. v o AC output voltage; v omax This represents the maximum AC output voltage. S 1~ S 4 and S d1 ~ S d4 All are switching transistors; i R This is the effective value of the current loop reference signal; K in The input phase signal coefficients; d o These are the control signals for the Boost converter; d feed This serves as a control signal feedforward for the Boost converter. u ac_rms The effective value of the AC input voltage; | u ac | represents the absolute value of the AC input voltage; v r ,v r_new1 , v r_new2 It is a modulated wave; v c_pos , v c_neg For stacked carrier v c The amplitude of the dividing line between the positive and negative half-cycles; v pos_top , v pos_bot , v neg_top , v neg_bot These are four groups of carrier signals; d s1 , d sd2 , d sd3 and d s4 These are switching transistors S1 and S2, respectively. d2 Switch S d3 And the drive signal for the switching transistor S4; K pL The power limiting factor is PI; PI stands for proportional-integral control; PWM stands for pulse width modulation. P in Input power to the converter; P o This refers to the converter's output power. θ The phase difference between the AC input and output voltages; θ 1 represents the phase difference between the AC input voltage and the AC input current; θ 2 represents the real-time phase of the AC input voltage or AC input current. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0029] Figure 1 The block diagram shows the control strategy for a combined AC / AC converter: This combined AC / AC converter consists of a passive rectifier bridge, a boost converter, and a DC / AC converter. The DC / AC converter includes switching transistors. S 1~ S 4. Switching transistor S d1 ~ S d4 Output inductor L o and output capacitor C o Switching transistorS 1. Drain connection to switching transistor S 3 drains, switching transistors S 2 source-connected switching transistors S 4 sources, switching transistors S d1 Source-connected switching transistor S d3 Source, switch S d1 Drain connection switching transistor S d2 Drain, switching transistor S d3 Drain connection switching transistor S d4 Drain, switching transistor S d2 Source and switching transistor S 1. Source and switch transistor S 2. Drain and output inductors L o Connected on the left, output inductor L o The output capacitor is connected on the right side. C o Positive terminal, output capacitor C o Negative electrode and switching transistor S 3. Source and Switch S 4. Drain and switching transistor S d4 Source and pole connected;

[0030] The converter configuration is as follows: the AC source is connected to the input of the passive rectifier bridge, the positive output of the passive rectifier bridge is connected to the positive input of the Boost converter, and the switching transistor of the DC / AC converter. S d1 Source, switch S d3 The source terminals are connected, and the positive output terminal of the Boost converter is connected to the switching transistor of the DC / AC converter. S 1. Drain and switching transistor S The drains are connected, and the negative output of the passive rectifier bridge is connected to the negative output of the Boost converter and the DC / AC converter. The output of the DC / AC converter is connected to the load.

[0031] Boost converter controls intermediate bus voltage V H and inductor current i B This includes the following steps:

[0032] Real-time sampling of intermediate bus voltage V H The intermediate bus voltage referenceV Href Subtract the intermediate bus voltage V H The error signal is obtained, and after processing by the PI controller, the effective value of the current loop reference signal is obtained. i R Sampled AC input voltage u ac And process it to obtain its absolute value | u ac |, and the input phase signal coefficients K in Multiply the two, and the result of multiplying them is the same as the effective value of the current loop reference signal. i R Multiplication generates a current loop reference signal i Bref Input phase signal coefficients K in The calculation formula is as follows:

[0033] ;

[0034] in u ac_rms Sampled AC input voltage u ac The processed effective value; it should be clarified that the current loop reference signal i Bref Essentially, it is an AC input current reference. i inref The specific derivation of the relevant parameters is as follows: Let the converter input power be... P in The effective value of the input current is i in_rms Its value is the same as the effective value of the current loop reference signal. i R equal, θ 1 represents the phase difference between the AC input voltage and the AC input current, and the active power control target. θ 1 = 0, therefore:

[0035] ;

[0036] The real-time phase of the AC input current is θ 2. Due to the inductor current of the Boost converter i B With rectified output current i L Hengzheng, therefore the AC input current reference i inref Since it is always positive, therefore we have:

[0037] ;

[0038] There is also a target for active power control. θ 1=0, therefore the real-time phase of the input voltage is also 1. θ 2, therefore we have:

[0039] ;

[0040] By combining the above three equations, we can obtain the AC input current reference. i inref Another expression:

[0041] ;

[0042] It can be observed that, after mathematical derivation, the AC input current reference... i inref Finally, the current loop reference signal in the current loop. i Bref Maintain consistency.

[0043] It should be noted that during the digital implementation of the controller, all voltage sampling signals are normalized using the internal voltage reference of the control chip. The voltage quantities involved in the control calculations within the controller are all per-unit values ​​(dimensionless pure digital values). Based on this, the absolute value of the AC input voltage inside the controller... u ac |A dimensionless quantity characterizing only the phase relationship, the effective value of the AC input voltage. u ac_rms The input phase signal coefficients are dimensionless quantities that characterize only the magnitude of the amplitude. K in It is also a dimensionless quantity characterizing the proportional calibration coefficient. Therefore, the formula for the current loop reference signal in the control loop is expressed as follows:

[0044] ;

[0045] in, i R The unit is A, | u ac |and K in All are dimensionless per-unit values, therefore i Bref The unit is also A, which is the same as the inductor current used in subsequent calculations. i B and rectified output current i L With consistent dimensions, each parameter can directly participate in closed-loop control calculations.

[0046] Current loop reference signal i Bref Subtract inductor currenti B With rectified output current i L The error signal is obtained, and this error signal is used to generate a control signal through a PI controller. d 0, control signal d 0 and control signal feedforward d feed The sums are then modulated by PWM and used as the drive signal for the switching transistor Q, thereby controlling the intermediate bus voltage. V H and inductor current i B The control, in which the control signal feedforward d feed The calculation formula is as follows:

[0047] ;

[0048] DC / AC converter controls AC output voltage v o and rectified output current i L The process includes the following steps: using stacked carriers with positive half-cycle amplitudes of 1 to 0 and negative half-cycle amplitudes of 0 to -1. v c Furthermore, the carrier frequencies for both positive and negative half-cycles are the same; the passive rectifier output voltage is sampled in real time. v L and intermediate bus voltage V H Multiply the carrier wave with a positive half-cycle amplitude of 1 to 0 by v L / V H Obtain carrier v pos_bot , 1- v pos_bot As a carrier v pos_top Therefore, two sets of carrier waves can be obtained during the positive half-cycle. v pos_bot and v pos_top Their dividing line is v L / V H ,use v c_pos This indicates that; similarly, the two sets of carriers in the negative half-cycle can be obtained. v neg_top and v neg_bot Their dividing line is - v L / V H ,use v c_neg This indicates that the superimposed carriers... v c Divided into four different carrier groups v pos_top , v pos_bot , v neg_top and v neg_bot Real-time sampling of AC output voltage v o AC output voltage reference v oref Subtract AC output voltage v o The error signal is obtained, and the obtained error signal is then passed through a PI controller to obtain a modulated wave. v r The modulated wave v r The amplitude ranges from -1 to 1;

[0049] When AC input voltage u ac With AC output voltage v o When in phase or out of phase, the system has no circulating current power, and the modulation principle waveform is as follows: Figure 2 As shown, the modulated wave v r With carrier v pos_top Intercepting the drive signal generated by the switching transistor S1 d s1 Switch S d1 Complementary to switch S1; Modulated wave v r With carrier v pos_bot Intersection generation of switching transistor S d2 drive signal d sd2 Switch S2 and switch S d2 Complementary; Modulated wave v r With carrier v neg_top Generate switching transistor S d3 drive signal d sd3 Switch S3 and switch S d3 Complementary; Modulated wave v r With carrier v neg_botIntercepting to generate the drive signal for switch S4 d s4 Switch S d4 Complementary to switch S4;

[0050] When AC input voltage u ac With AC output voltage v o At any phase that is neither in-phase nor out-of-phase, and the AC input current i in Less than the rectified output current i L At this time, reactive circulating current will appear in the system. It is particularly important to clarify that the generation of this reactive circulating current is subject to strict operating conditions: it only occurs when the output voltage of the passive rectifier is low. v L Near the zero point; while when the AC input voltage u ac With AC output voltage v o When in phase or out of phase, even if the passive rectifier output voltage is... v L Crossing the zero point will not lead to the generation of reactive circulating current, so there is no need to change the modulation waveform. Therefore, for the reactive circulating current power condition, the modulation principle waveform is as follows: Figure 3 As shown, AC input voltage u ac With AC output voltage v o The phase difference is π / 2, at which point the original modulated wave... v r Change to v r_new1 and v r_new2 Modulated wave v r_new1 and v r_new2 The driving signals for the switching transistors are generated by intersecting with different carrier waves, wherein the modulated wave... v r_new1 and v r_new2 Amplitude and power limiting factor K pL It can be obtained through the following calculations:

[0051] ;

[0052] Among them, the modulated wave v r_new1 and v r_new2 The amplitude is limited, with both ranging from -1 to 1.v omax This represents the maximum AC output voltage. v Lmax The maximum value of the passive rectified output voltage, and both are non-zero; at this time, the modulation wave v r_new1 With carrier v pos_top carrier v neg_top Intersection, generating switching transistors S1 and S2 respectively. d3 drive signal d s1 and d sd3 Switch S d1 And switching transistor S3 is connected to switching transistor S1 and switching transistor S2 respectively. d3 Complementary, modulated wave v r_new2 With carrier v pos_bot carrier v neg_bot Intersection, generating switching transistor S respectively d2 and the drive signal of the switching transistor S4 d sd2 and d s4 Switch S2 and switch S d4 Respectively with switching transistor S d2 It is complementary to switch S4. Therefore, when there is no circulating power in the system, the converter modulation wave is only generated by... v r Decision; when circulating power exists in the system, the converter modulation wave is determined by... v r_new1 and v r_new2 This decision allows the DC / AC converter to be applicable to input and output voltage conditions with arbitrary amplitude and phase.

[0053] Figure 4 The experimental waveform diagrams for the combined AC / AC converter are shown below. Figure 4 (a) shows the steady-state waveform when the AC input and output voltages are in phase. Figure 4 (b) shows the steady-state waveform when the phase difference between the AC input and output voltages is π / 4. Both can achieve a high AC input current sinusoidality of the converter, and the AC output voltage can maintain an ideal sinusoidal output. This proves that the combined AC / AC converter control method can optimize the power factor and improve the reliability of system operation.

[0054] Figure 5The efficiency comparison between the present invention and the traditional two-stage AC / AC power supply architecture shows that the efficiency of the present invention is superior to that of the traditional two-stage AC / AC power supply architecture across the entire load range, proving the effectiveness of the control method of the present invention in reducing the number of power transmission stages and improving system transmission efficiency.

[0055] Figure 6 The test results show the power factor of the AC input side of the combined AC / AC converter. Regardless of the phase relationship between the AC input and output voltages, the power factor on the AC input side remains above 0.99, demonstrating the effectiveness of this control method in optimizing the power factor.

[0056] In summary, this invention provides a control method for a combined AC / AC converter, which enables the combined AC / AC converter to have the technical advantages of small power conversion stages and excellent power factor, effectively improving system conversion efficiency, reducing system cost, improving power supply quality and enhancing system operational reliability.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A control method for a combined AC / AC converter, characterized in that: (1) The combined AC / AC converter is composed of a passive rectifier bridge, a boost converter and a DC / AC converter, wherein the DC / AC converter includes a switching transistor. S 1~ S 4. Switching transistor S d1 ~ S d4 Output inductor L o and output capacitor C o Switching transistor S 1. Drain connection to switching transistor S 3 drains, switching transistors S 2 source-connected switching transistors S 4 sources, switching transistors S d1 Source-connected switching transistor S d3 Source, switch S d1 Drain connection switching transistor S d2 Drain, switching transistor S d3 Drain connection switching transistor S d4 Drain, switching transistor S d2 Source and switching transistor S 1. Source and switch transistor S 2. Drain and output inductors L o Connected on the left, output inductor L o The output capacitor is connected on the right side. C o Positive terminal, output capacitor C o Negative electrode and switching transistor S 3. Source and Switch S 4. Drain and switching transistor S d4 Source and pole connected; The converter configuration is as follows: the AC source is connected to the input of the passive rectifier bridge, the positive output of the passive rectifier bridge is connected to the positive input of the Boost converter, and the switching transistor of the DC / AC converter. S d1 Source, switch S d3 With the source terminals connected, the positive output terminal of the Boost converter is connected to the switching transistor of the DC / AC converter. S 1. Drain and switching transistor S The drains are connected, and the negative output of the passive rectifier bridge is connected to the negative output of the Boost converter and the DC / AC converter. The output of the DC / AC converter is connected to the load. (2) Boost converter controls intermediate bus voltage V H and inductor current i B This includes the following steps: Real-time sampling of the intermediate bus voltage V H The intermediate bus voltage reference V Href Subtract the intermediate bus voltage V H The error signal is obtained, and after processing by the PI controller, the effective value of the current loop reference signal is obtained. i R Sampled AC input voltage u ac And process it to obtain its absolute value | u ac |, and the input phase signal coefficients K in Multiply the two, and the result of multiplying them is the same as the effective value of the current loop reference signal. i R Multiplication generates a current loop reference signal i Bref Input phase signal coefficients K in The calculation formula is as follows: ； in u ac_rms Sampled AC input voltage u ac The effective values ​​obtained after processing; i Bref Subtract inductor current i B With rectified output current i L The error signal is obtained, and this error signal is used to generate a control signal through a PI controller. d 0, control signal d 0 and control signal feedforward d feed The sums are then modulated by PWM and used as the drive signal for the switching transistor Q, thereby controlling the intermediate bus voltage. V H and inductor current i B The control, in which the control signal feedforward d feed The calculation formula is as follows: ； (3) DC / AC converter controls AC output voltage v o and rectified output current i L The process includes the following steps: using stacked carriers with positive half-cycle amplitudes of 1 to 0 and negative half-cycle amplitudes of 0 to -1. v c Furthermore, the carrier frequencies for both positive and negative half-cycles are the same; the passive rectifier output voltage is sampled in real time. v L and intermediate bus voltage V H Multiply the carrier wave with a positive half-cycle amplitude of 1 to 0 by v L / V H Obtain carrier v pos_bot , 1- v pos_bot As a carrier v pos_top Therefore, two sets of carrier waves can be obtained during the positive half-cycle. v pos_bot and v pos_top Their dividing line is v L / V H ,use v c_pos This indicates that; similarly, the two sets of carriers in the negative half-cycle can be obtained. v neg_top and v neg_bot Their dividing line is - v L / V H ,use v c_neg This indicates that the superimposed carriers... v c Divided into four different carrier groups v pos_top , v pos_bot , v neg_top and v neg_bot Real-time sampling of AC output voltage v o AC output voltage reference v oref Subtract AC output voltage v o The error signal is obtained, and the obtained error signal is then passed through a PI controller to obtain a modulated wave. v r The modulated wave v r The amplitude ranges from -1 to 1; when the AC input voltage... u ac With AC output voltage v o When in phase or out of phase, the system has no circulating power, and the modulated wave... v r With carrier v pos_top Intercepting the drive signal generated by the switching transistor S1 d s1 Switch S d1 Complementary to switch S1; Modulated wave v r With carrier v pos_bot Intersection generation of switching transistor S d2 drive signal d sd2 Switch S2 and switch S d2 Complementary; Modulated wave v r With carrier v neg_top Generate switching transistor S d3 drive signal d sd3 Switch S3 and switch S d3 Complementary; Modulated wave v r With carrier v neg_bot Intercepting the drive signal generated by the switching transistor S4 d s4 Switch S d4 Complementary to switch S4; when AC input voltage u ac With AC output voltage v o At any phase that is neither in-phase nor out-of-phase, and the AC input current i in Less than the rectified output current i L At this time, the system has reactive circulating power, and the original modulated wave v r Change to v r_new1 and v r_new2 Modulated wave v r_new1 and v r_new2 The driving signals for the switching transistors are generated by intersecting with different carrier waves, wherein the modulated wave... v r_new1 and v r_new2 Amplitude and power limiting factor K pL It can be obtained through the following calculations: ； Among them, the modulated wave v r_new1 and v r_new2 The amplitude is limited, with both ranging from -1 to 1. v omax This represents the maximum AC output voltage. v Lmax Both are non-zero, representing the maximum output voltage of the passive rectifier; modulated wave. v r_new1 With carrier v pos_top carrier v neg_top Intersection, generating switching transistors S1 and S2 respectively. d3 drive signal d s1 and d sd3 Switch S d1 And switching transistor S3 is connected to switching transistor S1 and switching transistor S2 respectively. d3 Complementary, modulated wave v r_new2 With carrier v pos_bot carrier v neg_bot Intersection, generating switching transistor S respectively d2 and the drive signal of the switching transistor S4 d sd2 and d s4 Switch S2 and switch S d4 Respectively with switching transistor S d2 Complementary to switch S4, therefore, when there is no circulating current power in the system, the converter modulation wave is only generated by... v r Decision; when circulating power exists in the system, the converter modulation wave is determined by... v r_new1 and v r_new2 This decision allows the DC / AC converter to be applicable to input and output voltage conditions with arbitrary amplitude and phase.

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