Dual-energy switching control method for LCC high-voltage generator

Abstract

The application provides a dual-energy switching control method for an LCC high-voltage generator. The method is based on the fundamental equivalent frequency domain model of a multiple voltage rectification LCC resonant converter, realizes fast solution of steady-state control parameters, establishes an accurate time domain mathematical model of the resonant cavity parallel capacitor voltage, designs a low-energy to high-energy transient switching control strategy, combines the actual working condition requirements, realizes system steady-state control in a state trajectory and PID combined manner, and rapidly discharges energy in the high-energy to low-energy transient process. The application combines the advantages of time domain control and frequency domain control, forms a composite control strategy suitable for multiple working conditions, can realize rapid dual-energy voltage switching within 100 mu s, ensures good output repeatability and control accuracy, and meets the actual engineering application requirements.

Description

Technical Field

[0001] This invention pertains to dual-energy switching control technology for multi-voltage rectifier LCC converters, specifically a dual-energy switching control method for LCC high-voltage generators. Background Technology

[0002] In dual-energy switching systems of multiplier rectifier (LCC) high-voltage generators, existing control methods mostly employ open-loop control based on experience-driven lookup tables or preset trajectories, as well as traditional PID closed-loop regulation. While these methods can achieve voltage switching under normal operating conditions, they still present several problems in practical applications. On the one hand, open-loop or experience-based control is poorly adaptable to changes in operating conditions. When load fluctuates or device parameters change, voltage overshoot or undershoot can easily occur, affecting output stability. On the other hand, traditional PID control often requires a trade-off between response speed and stability during rapid switching. Conservative parameters lead to slow switching speeds, while increasing the response can easily cause oscillations and overshoot. Furthermore, due to the strong nonlinear characteristics of the LCC resonant network, existing methods do not adequately consider its dynamic process, easily leading to resonance offset and output fluctuations during rapid voltage switching. Moreover, consistency is poor during multiple switching operations, making it difficult to meet the high requirements of speed and repeatability in applications such as medical CT. To address these issues, this invention proposes a novel dual-energy switching control strategy. Summary of the Invention

[0003] This invention proposes a dual-energy switching control method for LCC high-voltage generators.

[0004] The technical solution for achieving the present invention is: a dual-energy switching control method for an LCC high-voltage generator, comprising:

[0005] Step 1: Based on the high energy value and low energy value of the output voltage setting of the multi-voltage rectifier LCC high voltage generator, as well as the design parameters of the multi-voltage rectifier LCC high voltage generator, the predicted frequency value of the resonant cavity under the operating gain is obtained by using the improved fundamental wave analysis method.

[0006] Step 2: Quantitatively solve for the normalized values ​​of the predicted steady-state control parameter resonant cavity current corresponding to the high and low energy values ​​of the output voltage setting;

[0007] Step 3: Based on the normalized value of the resonant current prediction, the maximum value of the resonant cavity current, and the real-time detected input voltage, output voltage, and output current of the multiplier voltage rectifier LCC high voltage generator, calculate the predicted switching frequency for the initial stage of voltage establishment, as well as the predicted switching frequency for the final stage and the steady-state stage.

[0008] Step 4: Based on the predicted switching frequency values ​​for the initial stage, the final stage, and the steady-state stage, determine the switching frequency commands for the switching transistors of the multi-voltage rectifier LCC high-voltage generator during the transition from low-energy output voltage to high-energy output voltage and from high-energy output voltage to low-energy output voltage. Control the multi-voltage rectifier LCC high-voltage generator according to the determined switching frequency commands.

[0009] Compared with the prior art, the significant advantages of this invention are:

[0010] This invention addresses the inherent limitations of traditional state trajectory methods and fundamental wave approximation methods in modeling and control. It constructs a composite control architecture that integrates time-domain state trajectory models and fundamental wave analysis (FHA) to achieve a synergistic improvement in transient control performance and steady-state control accuracy. It enables dual-energy switching within 100µs with good repeatability, effectively reducing the radiation dose to patients.

[0011] This invention also designs a method for calculating steady-state resonant current to adjust steady-state control parameters, which effectively improves the accuracy of the system's steady-state voltage. The method for calculating steady-state resonant current also has high accuracy.

[0012] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0013] Figure 1 This is a voltage doubler rectifier LCC converter topology based on a multi-winding transformer.

[0014] Figure 2 This is a schematic diagram of the voltage and current waveforms during a switching cycle.

[0015] Figure 3 This is the first operating mode of the voltage doubler rectifier LCC converter.

[0016] Figure 4 This is the second operating mode of the voltage doubler rectifier LCC converter.

[0017] Figure 5 This is the third mode of operation for the voltage doubler rectifier LCC converter.

[0018] Figure 6 Establish the primary stage voltage trajectory for the voltage doubler rectifier LCC converter.

[0019] Figure 7 Establish the final stage and steady-state stage trajectories for the voltage of the voltage doubler rectifier LCC converter.

[0020] Figure 8 This is a schematic diagram of the control strategy.

[0021] Figure 9This is a simulation waveform for dual-energy switching.

[0022] Figure 10 The waveform is from a dual-energy switching experiment. Detailed Implementation

[0023] A dual-energy switching control method for LCC high-voltage generators addresses the inherent limitations of traditional state trajectory methods and fundamental wave approximation methods in modeling and control. It constructs a composite control architecture integrating a time-domain state trajectory model and the Free-Hybrid Ability (FHA) method, and designs a method for calculating the steady-state resonant current to adjust steady-state parameters, effectively improving the system's transient response and steady-state parameter solution capabilities. Based on this, and addressing the engineering requirements of rapid switching, high stability, and good repeatability of high-voltage power supplies, this invention further designs a dual-energy switching control scheme adaptable to multiple voltage levels, optimizing the switching logic and parameter configuration, while also being compatible with single-energy operation. Preliminary verification results show that the proposed scheme can achieve rapid switching at the microsecond level across multiple voltage levels. The specific steps are as follows:

[0024] Step 1: Set the output voltage of the multiplier rectifier LCC high voltage generator to the high energy value V. o-ref-high and output voltage setting low energy value V o-ref-low Output current setting value I o-ref And the design parameters of each component of the multiplier rectifier LCC high voltage generator, including the resonant cavity inductance L ss inductance value The resonant cavity series capacitor C ss capacitance value The resonant cavity is connected in parallel with capacitor C. pb capacitance value First voltage multiplier capacitor C o1b And the second voltage multiplier capacitor C o2b capacitance value Transformer turns ratio Number of voltage doubler rectifiers ;

[0025] The high-energy value V is set according to the output voltage of the multi-voltage rectifier LCC high-voltage generator. o-ref-high and output voltage setting low energy value V o-ref-low The design parameters of the multiplier rectifier LCC high-voltage generator were used, and the predicted frequency value f of the resonant cavity under the operating gain was obtained by using an improved fundamental frequency analysis method. set .

[0026] The topology of the multiplier voltage rectifier LCC high voltage generator is as follows: Figure 1 As shown, the voltage and current waveforms and mode diagrams within one switching cycle are as follows. Figure 2 .

[0027] The multi-voltage rectifier LCC high-voltage generator includes a DC power supply inverter bridge and a resonant cavity series capacitor C. ss Resonant cavity inductance L ss A transformer, B series-connected voltage multiplier rectifier modules, and a load; the resonant cavity is connected in series with capacitor C. ss One end of the resonant cavity inductor L is connected to one output port of the DC power supply inverter bridge. ss One end of the resonant cavity is connected to the other output port of the DC power inverter bridge, and the resonant cavity is connected in series with capacitor C. ss At the other end, the resonant cavity inductance L ss The other end is connected to both ends of the primary side of the transformer, and the secondary side of the transformer is connected to B series-connected voltage multiplier rectifier modules through a multi-winding transformer; the two ends of the load are connected to the first and last ends of the B series-connected voltage multiplier rectifier modules, and the B voltage multiplier rectifier modules have the same structure, including a resonant cavity and a parallel capacitor C. pb A voltage multiplier rectifier bridge, wherein the resonant cavity is connected in parallel with a capacitor C. pb The resonant cavity is connected in parallel with the secondary side of the transformer, and the parallel capacitor C is connected in parallel with the secondary side of the transformer. pb Both ends of the diode are connected to the input terminals of the voltage doubler rectifier bridge; the voltage doubler rectifier bridge includes a first diode D. 1b Second diode D 2b First voltage multiplier capacitor C o1b And the second voltage multiplier capacitor C o2b First diode D 1b The negative terminal of the second diode D 2b The positive terminal is connected to one end of the secondary side of the transformer, and the voltage multiplier capacitor C o1b The other end is connected to the second voltage multiplier capacitor C. o2b One end of the first diode D is connected to the other end of the secondary side of the transformer. 1b The positive terminal of the capacitor is connected to the first voltage multiplier capacitor C. o1b One end of the diode is connected to the load end, and the second diode D is connected to the load end. 2b The negative terminal is connected to the second voltage multiplier capacitor C. o2b The other end is connected to the other end of the load; the DC power inverter bridge includes a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4. The source of the first switch Q1 is connected to the positive terminal of the DC voltage source, and its drain is connected to the source of the second switch Q2 and the resonant cavity. The drain of the second switch Q2 is connected to the negative terminal of the DC voltage source. The source of the third switch Q3 is connected to the positive terminal of the DC voltage source, and its drain is connected to the source of the fourth switch Q4 and the resonant cavity. The drain of the fourth switch Q4 is connected to the negative terminal of the DC voltage source.

[0028] The multi-voltage rectifier LCC high-voltage generator has six modes:

[0029] In the first mode, during the time interval t0 to t1, the first switch Q1 and the fourth switch Q4 are turned on, while the second switch Q2 and the third switch Q3 remain off. In this case, the primary-side input voltage applied to the resonant network is V. in The resonant current flows from the rectifier bridge into the resonant cavity, and the resonant current only affects the capacitor C. pb Charging. All diodes are turned off.

[0030] The second mode occurs during the time interval t1 to t2, during which the first switch Q1 and the fourth switch Q4 are turned on, while the second switch Q2 and the third switch Q3 remain off. During this time period, the primary input voltage applied to the resonant network remains V. in The resonant current continues to flow from the rectifier bridge into the resonant cavity. The resonant current flows through the transformer and simultaneously affects the resonant capacitor C. pb and the first voltage multiplier capacitor C o1b Charging, at this time the first diode D 1b Forward bias and conduction.

[0031] The third mode occurs within the time interval t2 to t3. During this time period, the first switch Q1 and the fourth switch Q4 are off, while the second switch Q2 and the third switch Q3 are on. Therefore, the polarity of the primary-side input voltage applied to the resonant network is reversed to -V. in Although the voltage polarity is reversed, the input voltage is -V. in The resonant current continues to flow through the rectifier bridge, and the current simultaneously affects the resonant capacitor C. pb and the first voltage multiplier capacitor C o1b Charging, first diode D 1b It remains in the conductive state.

[0032] The fourth mode occurs during the time interval t3 to t4, during which the first switch Q1 and the fourth switch Q4 remain off, while the second switch Q2 and the third switch Q3 are on. In this case, the mode is symmetrically opposite to the first mode, and the primary-side input voltage applied to the resonant network is -V. in The resonant current flows from the rectifier bridge into the resonant cavity, and the resonant current only affects the resonant capacitor C. pb Reverse charging turns all diodes off.

[0033] The fifth mode occurs during the time interval t4 to t5, during which the first switch Q1 and the fourth switch Q4 remain off, while the second switch Q2 and the third switch Q3 are on. During this time period, the primary-side input voltage applied to the resonant network remains -V. in The resonant current continues to flow from the rectifier bridge into the resonant current, while simultaneously affecting capacitor C. pb Second voltage multiplier capacitor C o2b Charging, at this time the second diode D 2b Forward bias and conduction.

[0034] The sixth mode occurs within the time interval t5 to t6. During this time period, the first switch Q1 and the fourth switch Q4 are turned on, while the second switch Q2 and the third switch Q3 are turned off. Therefore, the polarity of the primary-side input voltage applied to the resonant network is reversed to V. in Despite the voltage polarity reversal, the resonant current continues to flow through the rectifier bridge, similar to the third mode, while simultaneously affecting the resonant capacitor C. pb Second voltage multiplier capacitor C o2b Charging causes the second diode D to... 2b Maintain the conductive state.

[0035] Based on the operating characteristics of the LCC high-voltage generator, an accurate mathematical model of the frequency gain is constructed using the fundamental equivalent method to determine the corresponding angular frequency. Based on this, the steady-state control parameters, i.e., the predicted frequency value f of the resonant cavity, are calculated. set ;

[0036] The specific mathematical model for the frequency gain is as follows:

[0037] (1)

[0038] in, For output voltage, Input voltage, Indicates the gain of the resonant network. The voltage V of the parallel capacitor in the resonant cavity of the first voltage doubler rectifier bridge Cp1 The normalized basis amplitude of (t). and The calculation formula is as follows:

[0039]

[0040]

[0041]

[0042] In the formula, and They are respectively Figure 10 The equivalent resistance and equivalent capacitance in the equivalent model of the rectifier bridge shown. A capacitor connected in parallel to the resonant cavity The capacitance value of a capacitor. and The voltage V of the parallel capacitor in the resonant cavity of the first voltage doubler rectifier bridge is respectively. Cp1 With the inverter bridge output square wave voltage V AB The fundamental component of and The parallel voltage V of the resonant cavity of the first voltage doubler rectifier bridge Cp1N The sine and cosine amplitudes of the fundamental component of (t); Angular frequency, and These represent the real and imaginary parts of the resonant network gain, respectively.

[0043] Calculate the predicted frequency value f of the cavity based on the angular frequency. set :

[0044]

[0045] Step 2: Set the high-energy value V for the output voltage. o-ref-high and output voltage setting low energy value V o-ref-low Normalized value of the corresponding steady-state control parameter resonant cavity current prediction The quantitative solution is performed as follows:

[0046] First, the internal state of the resonant cavity is solved using time-domain analysis, and the voltage values ​​of the parallel capacitor of the first voltage doubler rectifier bridge at the end time t1 of the first mode and the end time t3 of the third mode are accurately calculated. as well as :

[0047]

[0048]

[0049] In the formula, This is the capacitance value of the voltage multiplier capacitor. For output current, The conduction angle of the voltage doubler rectifier diode can be calculated iteratively using the following formula.

[0050]

[0051] Based on charge conservation, the voltage values ​​of the resonant cavity series capacitor at the end time t1 of the first mode and the end time t3 of the third mode are determined. as well as :

[0052]

[0053]

[0054] By combining the resonant waveform and the symmetry characteristics of each mode state trajectory, the corresponding circuit states are derived and solved, and finally the normalized voltage can be obtained. The specific form is as follows:

[0055]

[0056] In the formula, This represents the voltage value of the resonant cavity series capacitor at the end time t1 of the first mode.

[0057] Based on geometric relationships, the resonant cavity current at time t1 is first solved, and its expression is:

[0058]

[0059] Based on this, further derivation yields the normalized value of the predicted steady-state control parameter, the resonant cavity current. The specific calculation formula is as follows:

[0060]

[0061] In the further implementation process, the state trajectory of each mode is plotted with the normalized value of the resonant cavity current as the vertical axis and the normalized value of the combined voltage as the horizontal axis. The combined voltage refers to the sum of the voltage of the resonant cavity series capacitor and the voltage of the resonant cavity parallel capacitor.

[0062] The mathematical model of the state trajectory is as follows. Taking the first voltage doubler rectifier bridge as an example, the time-domain model of each mode of each voltage doubler rectifier bridge is the same, and is as follows:

[0063] First mode such as Figure 3 ,

[0064]

[0065]

[0066] The combined voltage The voltage V of the resonant cavity series capacitor Cs (t) Voltage of the capacitor V connected in parallel with the resonant cavity Cp The sum of (t). This is the first modal angular frequency, which is related to the operating parameters. This represents the combined voltage at time t0.

[0067] Second mode such as Figure 4 ,

[0068]

[0069]

[0070] coefficients in time-domain equations , , , , It is related to the initial conditions. , Depending on the resonant element parameters and the number of voltage doubler rectifier stages, The calculated second modal angular frequency is related to the operating parameters.

[0071] Third mode such as Figure 5 ,

[0072]

[0073]

[0074] This represents the combined voltage at time t1.

[0075] Based on the modal symmetry and the relationship of third-order functions, equations (13) and (14) are processed to obtain the trajectories of the first and fourth modes, respectively:

[0076]

[0077]

[0078] Processing equations (15) and (16) yields the trajectories of the second and fifth modes, respectively:

[0079]

[0080]

[0081] Processing equations (17) and (18), the trajectories of the third and sixth modes are obtained as follows:

[0082]

[0083]

[0084] in, This is the normalized value of the resonant cavity current. This is the normalized value of the combined voltage;

[0085] The intersection points of the modal state trajectories during the initial stage of voltage establishment are marked as W, X, Y, and Z, where W is the intersection point of the sixth mode trajectory and the first mode trajectory; X is the intersection point of the first mode trajectory and the second mode trajectory; Y is the intersection point of the second mode trajectory and the third mode trajectory; and Z is the intersection point of the third mode trajectory and the fourth mode trajectory, with coordinates W(V) and Z(Y). W ,0),X (V X ,I X ), Y (V Y , I maxN ), Z (V Z , 0), This represents the maximum value of the resonant cavity current.

[0086] The initial voltage setup phase is when the output voltage is lower than the first threshold percentage of the high-energy value set for the output voltage.

[0087] The intersection points of the final stage and steady-state trajectory are W', X', Y', and Z', respectively, where W' is the intersection of the sixth mode trajectory and the first mode trajectory; X' is the intersection of the first mode trajectory and the second mode trajectory; Y' is the intersection of the second mode trajectory and the third mode trajectory; and Z' is the intersection of the third mode trajectory and the fourth mode trajectory, with coordinates W'(V'). W , 0)X'(V' X , I' X ), Y'(V' Y , I setN ), Z'(V' Z , 0, let the radius of the arc segment X'Y' be denoted as The radius of the arc segment Y'Z' is denoted as ;

[0088] The final stage and steady-state stage are the stages where the output voltage is higher than the first threshold percentage of the set high energy value of the output voltage and the output voltage is constant at the set high energy value of the output voltage.

[0089] Step 3: Normalized value based on the resonant current prediction And the maximum value of the resonant cavity current that acts as a constraint. Real-time monitoring of the input voltage of the multi-voltage rectifier LCC high-voltage generator. Output voltage and output current The predicted switching frequency for the initial stage of voltage establishment was calculated. And the predicted switching frequency values ​​for the final stage and steady-state stage. The initial voltage setup phase occurs when the output voltage is lower than the set output voltage value V. o-ref-high The 60% stage, the final stage, and the steady-state stage are characterized by the output voltage being higher than the set output voltage V. o-ref-high The 60% stage and the steady-state stage are defined by the following methods:

[0090] like Figure 6 As shown, the design voltage establishes the predicted switching frequency value in the initial stage. The calculation process is as follows:

[0091] The intersection points of the initial stage state trajectories established by voltage are labeled W, X, Y, and Z, where W is the intersection point of the sixth mode trajectory and the first mode trajectory; X is the intersection point of the first mode trajectory and the second mode trajectory; Y is the intersection point of the second mode trajectory and the third mode trajectory; and Z is the intersection point of the third mode trajectory and the fourth mode trajectory, with coordinates W(V) and Z(Y). W ,0),X (V X ,I X ), Y (V Y , I maxN ), Z (V Z , 0), The maximum value of the resonant cavity current that provides confinement can be derived from symmetry, V. W With V Z They are equal. Let the radius of the arc in segment XY be denoted as... The radius of the arc in segment YZ is denoted as The following relationship exists in the process from W to X;

[0092]

[0093] The capacitor C in parallel with the resonant cavity pb Parameter values;

[0094] Furthermore, based on the geometric relationships corresponding to the trajectories, the following expression can be derived:

[0095]

[0096] In the formula, The vertical coordinate of point X in the state trajectory diagram; The first impedance, This is the second impedance;

[0097] To simplify the calculation definition:

[0098]

[0099] Solving equations (26) and (27) simultaneously yields the expression for the trajectory parameters, as shown below:

[0100]

[0101] The arc angle between the intersection point W and X is denoted as The elliptical arc angle between points X and Y is denoted as . The arc angle between points Y and Z is denoted as The specific expressions for each of the above angles are given by the following formulas.

[0102]

[0103] The on-time and operating frequency of the switching transistor corresponding to the three trajectories can be further derived. The trajectory corresponding to the first mode is the elliptical mode portion, with the resonant angular frequency denoted as... The trajectories corresponding to the second and third modes are circular arc trajectories with resonant angular frequencies of . .

[0104] Based on the above analysis, the following expression is obtained:

[0105]

[0106] This represents the predicted switching frequency value in the initial stage.

[0107] Predicted switching frequency values ​​during the final voltage build-up and steady-state phases of the design voltage The calculation process is as follows:

[0108] like Figure 7 As shown, the peak value of the resonant current in the final stage and steady-state stage occurs during the second mode, corresponding to the radius of the arc segment X'Y'. The intersection points of the state trajectories are relabeled as W', X', Y', and Z', where W' is the intersection point of the sixth mode trajectory and the first mode trajectory; X' is the intersection point of the first mode trajectory and the second mode trajectory; Y' is the intersection point of the second mode trajectory and the third mode trajectory; and Z' is the intersection point of the third mode trajectory and the fourth mode trajectory, with coordinates W'(V') and Z'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''" ""' ... W , 0)X'(V' X , I' X ), Y'(V' Y , I setN ), Z'(V' Z , 0), and by the symmetry, V' can also be deducedW With V' Z They are equal. Let the radius of the arc segment X'Y' be denoted as... The radius of the arc segment Y'Z' is denoted as From W' to X', the following relationship can be derived:

[0109]

[0110] In the formula, The vertical coordinate of point X' in the state trajectory diagram;

[0111] Solving the simultaneous equations (19) yields the expression for the trajectory parameters at this stage, as shown below:

[0112]

[0113] Similarly, the arc angle between the intersection points W' and X' is denoted as... The elliptical arc angle between points X' and Y' is denoted as . The arc angle between points Y' and Z' is denoted as The specific expressions for each of the above angles are given by the following formulas:

[0114]

[0115] Similarly, the on-time of the switching transistor and its operating frequency can be integrated to obtain the following expression:

[0116]

[0117] These are the predicted switching frequencies for the final stage and the steady-state stage.

[0118] Step 4: Based on the above steady-state and transient designs, a complete control method for the dual-energy switching of the system is combined. This involves the preceding derivation, plus the process of turning off the switching transistor to release energy when switching from high energy to low energy. The overall control logic is as follows:

[0119] Its core consists of a frequency model based on fundamental wave analysis, a time-domain state trajectory control module, and a PID controller. This control strategy addresses the dynamic response requirements of the converter under different energy levels and load conditions, integrating feedforward prediction and closed-loop regulation mechanisms to achieve fast and stable control. The specific control process selected for different voltage conditions is as follows:

[0120] Step 4.1: Set the output voltage to the high-energy value V o-ref-high and output voltage setting low energy value V o-ref-lowThese are respectively voltage-controlled high-energy and low-energy targets. During the voltage switching process from low to high energy, the predicted switching frequency value obtained in step 3 for the initial stage is... The switching frequency is controlled by the switching frequency command to achieve rapid startup.

[0121] When the output voltage reaches the set high energy value V o-ref-high To further improve steady-state accuracy and suppress the effects of parameter disturbances and modeling errors, a PID module can be connected when the output voltage V reaches 80%. o With the output voltage set to high energy value V o-ref-high The error between the two signals is introduced into the PID controller. The PID controller generates a frequency correction Δf based on this error signal. sw The final stage of step 3 and the predicted switching frequency values ​​of the steady-state stage are superimposed to form the final high-energy steady-state switching frequency command f. sw ; and with f sw The switching frequency of the horizontal switching transistor is controlled to improve steady-state accuracy.

[0122] Step 4.2: During the high-energy to low-energy voltage switching process, all switching transistors are turned off to quickly release the energy of the resonant cavity and improve the switching speed from high energy to low energy.

[0123] When the output voltage reaches the set low energy value, in order to improve steady-state accuracy and suppress the influence of parameter disturbances and modeling errors, the predicted switching frequency values ​​for the final stage and steady-state stage will be adjusted. and output voltage V o Compared with reference value V o-ref-low The error between the two signals is introduced into the PID controller. The PID controller generates a frequency correction Δf based on this error signal. sw The frequency correction amount Δf sw With low-energy feedforward prediction frequency Combined with the switching frequency command f in low-energy steady state sw and with f sw The switching frequency of the horizontal switching transistor is controlled to improve steady-state accuracy.

[0124] The subsequent process maintains a loop from step 4.1 to step 4.2, and the overall control process is as follows: Figure 8 The control strategy diagram.

[0125] Figure 9 Figure 10 The simulation and experimental waveforms obtained by this invention are shown respectively. The designed control scheme can achieve rapid voltage switching within 100 microseconds under multiple voltage levels and has good repeatability.

Claims

1. A dual-energy switching control method for an LCC high-voltage generator, characterized in that, include: Step 1: Based on the high energy value and low energy value of the output voltage setting of the multi-voltage rectifier LCC high voltage generator, as well as the design parameters of the multi-voltage rectifier LCC high voltage generator, the predicted frequency value of the resonant cavity under the operating gain is obtained by using the improved fundamental wave analysis method. Step 2: Quantitatively solve for the normalized values ​​of the predicted steady-state control parameter resonant cavity current corresponding to the high and low energy values ​​of the output voltage setting; Step 3: Based on the normalized value of the resonant current prediction, the maximum value of the resonant cavity current, and the real-time detected input voltage, output voltage, and output current of the multiplier voltage rectifier LCC high voltage generator, calculate the predicted switching frequency for the initial stage of voltage establishment, as well as the predicted switching frequency for the final stage and the steady-state stage. Step 4: Based on the predicted switching frequency values ​​for the initial stage, the final stage, and the steady-state stage, determine the switching frequency commands for the switching transistors of the multi-voltage rectifier LCC high-voltage generator during the transition from low-energy output voltage to high-energy output voltage and from high-energy output voltage to low-energy output voltage. Control the multi-voltage rectifier LCC high-voltage generator according to the determined switching frequency commands.

2. The dual-energy switching control method for LCC high-voltage generator according to claim 1, characterized in that, The multi-voltage rectifier LCC high-voltage generator includes a DC power supply inverter bridge and a resonant cavity series capacitor (C). ss ), resonant cavity inductance (L ss The resonant cavity includes a transformer, B series-connected voltage multiplier rectifier modules, and a load, along with a series capacitor (C). ss One end of the resonant cavity inductor (L) is connected to one output port of the DC power supply inverter bridge. ss One end of the resonant cavity is connected to the other output port of the DC power supply inverter bridge, and the resonant cavity is connected in series with a capacitor (C). ss At the other end of the resonant cavity, the inductance (L) ss The other end of the load is connected to both ends of the primary side of the transformer, and the secondary side of the transformer is connected to B series-connected voltage multiplier rectifier modules through a multi-winding transformer; the two ends of the load are connected to the first and last ends of the B series-connected voltage multiplier rectifier modules respectively, and the B voltage multiplier rectifier modules have the same structure, including a resonant cavity and a parallel capacitor (C). pb ), voltage multiplier rectifier bridge, and the resonant cavity parallel capacitor (C) pb The resonant cavity is connected in parallel with the secondary side of the transformer, and the capacitor (C) in parallel with the resonant cavity is connected in parallel with the secondary side of the transformer. pb Both ends of the diode are connected to the input terminals of the voltage doubler rectifier bridge; the voltage doubler rectifier bridge includes a first diode (D). 1b ), second diode (D) 2b ), first voltage multiplier capacitor (C) o1b ) and the second voltage multiplier capacitor (C o2b ), first diode (D 1b The negative terminal of the first diode (D) and the second diode (D) 2b The positive terminal of the capacitor is connected to one end of the secondary side of the transformer, and the first voltage multiplier capacitor (C) o1b The other end of the capacitor is connected to the second voltage multiplier capacitor (C). o2b One end of the first diode (D) is connected to the other end of the secondary side of the transformer. 1b The positive terminal of ) and the first voltage multiplier capacitor (C) o1b One end of the second diode (D) is connected to the load end. 2b The negative terminal of ) is connected to the second voltage multiplier capacitor (C) o2b The other end of the DC power supply inverter bridge is connected to the other end of the load; the DC power supply inverter bridge includes a first switch (Q1), a second switch (Q2), a third switch (Q3), and a fourth switch (Q4). The source of the first switch (Q1) is connected to the positive terminal of the DC voltage source, the drain of the first switch (Q1) is connected to the source of the second switch (Q2) and the resonant cavity, the drain of the second switch (Q2) is connected to the negative terminal of the DC voltage source, the source of the third switch (Q3) is connected to the positive terminal of the DC voltage source, the drain of the third switch (Q3) is connected to the source of the fourth switch (Q4) and the resonant cavity, and the drain of the fourth switch (Q4) is connected to the negative terminal of the DC voltage source.

3. The dual-energy switching control method for LCC high-voltage generator according to claim 2, characterized in that, The multi-voltage rectifier LCC high-voltage generator has six modes: The first mode occurs within the time interval t0 to t1, during which the first switch (Q1) and the fourth switch (Q4) are turned on, while the second switch (Q2) and the third switch (Q3) remain off. During this time interval, the primary input voltage of the resonant network is V. in The resonant current flows from the rectifier bridge into the resonant cavity, and the resonant current only affects the parallel capacitor (C) of the resonant cavity. pb When charging, all diodes are turned off. This is the input voltage for the LCC high-voltage generator; The second mode occurs during the time interval t1 to t2, during which the first switch (Q1) and the fourth switch (Q4) are turned on, while the second switch (Q2) and the third switch (Q3) remain off. During this time period, the primary input voltage applied to the resonant network remains V. in The resonant current continues to flow from the rectifier bridge into the resonant cavity, and the resonant current flows through the transformer, while simultaneously affecting the parallel capacitor (C) of the resonant cavity. pb ) and the first voltage multiplier capacitor (C o1b (Charging) At this time, the first diode D 1b Forward bias and conduction; The third mode occurs within the time interval t2 to t3. During this time period, the first switch (Q1) and the fourth switch (Q4) are turned off, while the second switch (Q2) and the third switch (Q3) are turned on. During this time period, the polarity of the primary-side input voltage applied to the resonant network is reversed to -V. in The resonant current continues to flow through the rectifier bridge, and the current simultaneously affects the parallel capacitor (C) of the resonant cavity. pb ) and the first voltage multiplier capacitor (C o1b ) charging, first diode (D 1b It remains in the conductive state; The fourth mode occurs during the time interval t3 to t4, during which the first switch (Q1) and the fourth switch (Q4) remain off, while the second switch (Q2) and the third switch (Q3) are on. During this time period, the primary input voltage applied to the resonant network is -V. in The resonant current flows from the rectifier bridge into the resonant cavity, and the resonant current only affects the parallel capacitor (C) of the resonant cavity. pb Reverse charging turns off all diodes; The fifth mode occurs during the time interval t4 to t5, during which the first switch (Q1) and the fourth switch (Q4) remain off, while the second switch (Q2) and the third switch (Q3) are on. During this time period, the primary input voltage applied to the resonant network remains -V. in The resonant current continues to flow from the rectifier bridge into the resonant cavity, while simultaneously affecting the parallel capacitor (C) of the resonant cavity. pb ) and second voltage multiplier capacitor (C) o2b ) is charging, at which time the second diode (D) is charging. 2b Forward bias and conduction; The sixth mode occurs within the time interval t5 to t6. During this time period, the first switch (Q1) and the fourth switch (Q4) are turned on, while the second switch (Q2) and the third switch (Q3) are turned off. During this time period, the polarity of the primary-side input voltage applied to the resonant network is reversed to V. in The resonant current continues to flow through the rectifier bridge, similar to the third mode, while simultaneously affecting the parallel capacitor (C) of the resonant cavity. pb ) and second voltage multiplier capacitor (C) o2b ) Charges the second diode D 2b Maintain the conductive state.

4. The dual-energy switching control method for LCC high-voltage generator according to claim 2, characterized in that, The intersection points of the modal state trajectories in the initial stage of voltage establishment are marked as W, X, Y, and Z, where W is the intersection point of the sixth mode trajectory and the first mode trajectory; X is the intersection point of the first mode trajectory and the second mode trajectory. Where Y is the intersection of the second-mode trajectory and the third-mode trajectory; Z is the intersection of the third-mode trajectory and the fourth-mode trajectory, with coordinates W(V) and W(V). W ,0),X (V X ,I X ), Y(V Y , I maxN ), Z (V Z , 0), This represents the maximum value of the resonant cavity current. The initial voltage setup phase is when the output voltage is lower than the first threshold percentage of the high-energy value set for the output voltage. The intersection points of the final stage and steady-state trajectory are W', X', Y', and Z', respectively, where W' is the intersection point of the sixth mode trajectory and the first mode trajectory; Where X' is the intersection of the first mode trajectory and the second mode trajectory; Where Y' is the intersection of the second-mode trajectory and the third-mode trajectory; Where Z' is the intersection of the third mode trajectory and the fourth mode trajectory, with coordinates W'(V') and W'(V') respectively. W , 0)X'(V' X , I' X ), Y'(V' Y , I setN ), Z'(V' Z , 0, let the radius of the arc segment X'Y' be denoted as The radius of the arc segment Y'Z' is denoted as ; The final stage and steady-state stage are the stages where the output voltage is higher than the first threshold percentage of the set high energy value of the output voltage and the output voltage is constant at the set high energy value of the output voltage.

5. The dual-energy switching control method for an LCC high-voltage generator according to claim 3, characterized in that, The trajectory of each modal state is plotted with the normalized value of the resonant cavity current as the vertical axis and the normalized value of the voltage as the horizontal axis.

6. The dual-energy switching control method for an LCC high-voltage generator according to claim 4, characterized in that, The specific method for obtaining the predicted frequency value of the resonant cavity under the operating gain using the improved fundamental wave analysis method is as follows: The fundamental wave equivalent method is used to construct a frequency gain mathematical model to determine the angular frequency corresponding to the frequency. The frequency gain mathematical model is as follows: ； in, This is the output voltage of the LCC high-voltage generator. This is the input voltage for the LCC high-voltage generator. Indicates the gain of the resonant network. This is the normalized fundamental amplitude of the voltage across the parallel capacitor in the resonant cavity of the first voltage doubler rectifier bridge. The specific gain of the resonant network is as follows: ； ； In the formula, This is the fundamental component of the voltage across the parallel capacitor in the resonant cavity of the first voltage doubler rectifier bridge. The inverter bridge outputs a square wave voltage V. AB The fundamental component of For transformer turns ratio, This refers to the number of voltage doubler rectifiers; and These are the equivalent resistance and equivalent capacitance in the equivalent model of the rectifier bridge, respectively. This is the capacitance value of the capacitor connected in parallel to the resonant cavity; Angular frequency, and These represent the real and imaginary parts of the resonant network gain, respectively. The inductance value of the resonant cavity inductor. This is the capacitance value of the capacitor connected in series with the resonant cavity; Calculate the predicted frequency value f of the cavity based on the angular frequency. set : 。 7. The dual-energy switching control method for an LCC high-voltage generator according to claim 4, characterized in that, The specific method for quantitatively solving the normalized value of the predicted steady-state control parameter resonant cavity current corresponding to the high and low energy values ​​of the output voltage setting is as follows: The internal state of the resonant cavity is solved using time-domain analysis, and the voltage values ​​of the parallel capacitor of the first voltage doubler rectifier bridge at the end time t1 of the first mode and the end time t3 of the third mode are calculated. as well as Specifically, they are: ； ； In the formula, This is the output voltage of the LCC high-voltage generator. Angular frequency, The number of voltage doubler rectifiers. For output current, This is the capacitance value of the voltage multiplier capacitor. This is the conduction angle of the voltage multiplier rectifier diode; Based on charge conservation, the voltage values ​​of the resonant cavity series capacitor at the end time t1 of the first mode and the end time t3 of the third mode are determined. as well as : ； ； In the formula, For transformer turns ratio, This is the capacitance value of the capacitor connected in parallel to the resonant cavity. This is the capacitance value of the capacitor connected in parallel to the resonant cavity. This is the capacitance value of the capacitor connected in series with the resonant cavity. This is the equivalent resistance value of the load. The voltage value of the parallel capacitor of the resonant cavity at the end time t3 of the third mode. This is the capacitance value of the voltage multiplier capacitor; Based on the resonant waveform and the symmetry characteristics of each mode state trajectory, the normalized voltage is calculated. : ； In the formula, This is the input voltage for the LCC high-voltage generator. This represents the voltage value of the resonant cavity series capacitor at the end time t1 of the first mode. The resonant cavity current at time t1, the end of the first mode, is solved based on geometric relationships, specifically as follows: ； In the formula, , , Let X'Y' be the radius of the arc segment. The first impedance, This is the second impedance; Normalized values ​​for calculating the predicted steady-state control parameters and resonant cavity current. The specific calculation formula is as follows: 。 8. The dual-energy switching control method for an LCC high-voltage generator according to claim 4, characterized in that, The predicted switching frequency for the initial stage of voltage setup is calculated. The specific method is as follows: Let the radius of the arc segment XY be denoted as . The radius of the arc in segment YZ is denoted as The following relationship exists in the process from W to X; ； In the formula, This is the capacitance value of the capacitor connected in parallel to the resonant cavity. This is the output voltage of the LCC high-voltage generator. This is the input voltage for the LCC high-voltage generator. For transformer turns ratio, The number of voltage doubler rectifiers. This is the capacitance value of the capacitor connected in series with the resonant cavity. This is the capacitance value of the capacitor connected in parallel to the resonant cavity; Based on the geometric relationship corresponding to the trajectory, the following expression is determined: ； 、 ； In the formula, The vertical coordinate of point X in the state trajectory diagram; The first impedance, This is the second impedance; To simplify the calculation definition: ； It is the capacitance value of the parallel capacitor of the resonant cavity; The expression for the trajectory parameters is obtained as follows: ； The arc angle between the intersection point W and X is denoted as The elliptical arc angle between the intersection points X and Y is denoted as . The arc angle between points Y and Z is denoted as ; ； The resonant angular frequency of the trajectory corresponding to the first mode is denoted as . ; The trajectories corresponding to the second and third modes are circular arc trajectories, with a resonant angular frequency of [missing value]. ; Therefore, the predicted switching frequency for the initial stage of voltage setup is calculated: 。 9. The dual-energy switching control method for an LCC high-voltage generator according to claim 8, characterized in that, The predicted switching frequencies for the final and steady-state stages are as follows: In the process from W' to X', the following relationship is determined: ； In the formula, The ordinate of point X' in the state trajectory diagram The expression for the trajectory parameters at this stage is as follows: ； The arc angle between the intersection points W' and X' is denoted as The elliptical arc angle between points X' and Y' is denoted as . The arc angle between points Y' and Z' is denoted as ; The combined on-time and operating frequency of the switching transistor are as follows: ； In the formula, These are the predicted switching frequencies for the final stage and the steady-state stage.

10. The dual-energy switching control method for an LCC high-voltage generator according to claim 1, characterized in that, The specific method for determining the switching frequency command of the multiplier rectifier LCC high-voltage generator switching transistor during the transition from a low-energy output voltage setting to a high-energy output voltage setting, and during the transition from a high-energy output voltage setting to a low-energy output voltage setting, is as follows: When the LCC high voltage generator output voltage switches from low energy to high energy, the predicted value of the switching frequency in the primary stage will be used. The switching frequency of the LCC high voltage generator switching tube is controlled as a switching frequency command. When the output voltage reaches the set percentage of the high energy value of the output voltage setting, the output voltage V will be... o With the output voltage set to high energy value V o-ref-high The error between them is introduced into the PID controller. The PID controller generates a frequency correction amount based on the error signal. The frequency correction amount of the predicted switching frequency in the final stage and the steady-state stage is superimposed as the switching frequency command to control the switching frequency of the LCC high voltage generator switching tube. When the output voltage of the LCC high voltage generator switches from high energy to low energy, all switching transistors are turned off. When the output voltage reaches the set low energy value, the predicted switching frequency values ​​for the final stage and steady-state stage will be... and output voltage V o Compared with reference value V o-ref-low The error between them is introduced into the PID controller. The PID controller generates a frequency correction amount based on the error signal. The predicted switching frequency values ​​of the final stage and the steady-state stage are superimposed with the frequency correction amount to form a switching frequency command to control the switching frequency of the LCC high voltage generator switching tube.

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