Control method of high voltage generator

Abstract

The invention provides a control method of a high-voltage generator. The control method comprises the following steps: acquiring resonance current of the high-voltage generator; determining the sampling time of each period of the resonance current according to the resonance current; and according to the sampling time of each period, the target acquisition circuit and the target acquisition signal in the target acquisition circuit, sampling the target acquisition signal to obtain a resonance current characteristic quantity, and taking the resonance current characteristic quantity as an inner loop feedback value for controlling the high-voltage generator. The target acquisition signal in the target acquisition circuit is acquired at the sampling moment, the acquired target acquisition signal is used as the resonance current characteristic quantity, the fluctuation of the resonance current characteristic quantity is very small, and a high-speed ADC does not need to be matched. The method not only can be used for acquiring the resonant current characteristic quantity of the fixed-frequency resonant converter, but also can be used for acquiring the resonant current characteristic quantity of the variable-frequency resonant converter, and particularly, the resonant current characteristic quantity acquired in the variable-frequency resonant converter is more accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of high voltage generators, and in particular to a control method of a high voltage generator. Background Art

[0002] X-ray imaging equipment includes a high-voltage generator, which includes a main power part and an auxiliary power part. The main power part can output a high voltage such as several thousand volts, and the auxiliary power part can output a lower voltage. The main power part of the high-voltage generator often uses a resonant converter, and the resonant converter usually uses the resonant current as a closed-loop control parameter during control. The resonant current is a physical quantity with a frequency that can reach tens of kHz to hundreds of kHz, and the real-time value fluctuates greatly. This physical quantity needs to be processed before it can be used in the controller.

[0003] The resonant converter used in the high-voltage generator can be divided into a fixed-frequency resonant converter and a variable-frequency resonant converter according to different modulation methods. For these two types of resonant converters, one prior art is to use the absolute value of the resonant current directly as feedback control, or to use it as feedback control after analog or digital filtering. For the fixed-frequency resonant converter, another prior art is to use the resonant current as feedback control after periodic averaging. However, the feedback control method of the current prior art causes the resonant converter control to have large fluctuations and unstable output voltage. Especially for the resonant converter working with variable frequency, the feedback control effect is very poor. Summary of the invention

[0004] The invention provides a control method for a high voltage generator to solve the technical problem of large fluctuation of a resonance current characteristic quantity.

[0005] In order to solve the above technical problems, the present invention provides a control method of a high voltage generator, comprising the following steps:

[0006] Obtaining the resonant current of the high voltage generator;

[0007] Determining a sampling time of each cycle of the resonant current according to the resonant current;

[0008] According to the sampling time of each cycle, the target acquisition circuit and the target acquisition signal in the target acquisition circuit, the target acquisition signal is sampled to obtain a resonant current characteristic quantity, and the resonant current characteristic quantity is used as an inner loop feedback value for controlling the high voltage generator.

[0009] Optionally, the step of determining the sampling moment of each cycle of the resonant current according to the resonant current includes: determining the sampling moment of the corresponding cycle of the resonant current according to the moment when the resonant current is equal to zero in each cycle of the resonant current.

[0010] Optionally, the step of determining the sampling moment of each cycle of the resonant current based on the resonant current includes: converting the resonant current into an electrical signal whose phase is ahead of the resonant current, and determining the sampling moment of the corresponding cycle of the resonant current based on the moment when the electrical signal is equal to zero in each cycle.

[0011] Optionally, the target acquisition circuit is a preset capacitor charging and discharging circuit, and the capacitor charging and discharging circuit includes a capacitor;

[0012] One end of the capacitor is used to input the resonant current, and the other end of the capacitor is connected to the ground;

[0013] A switch control signal is determined based on the resonant current and the sampling time, and the switch of the capacitor charging and discharging circuit is controlled according to the switch signal to charge and discharge the capacitor; at the sampling time, the maximum value of the capacitor voltage across the capacitor is collected, and the maximum value of the capacitor voltage is used as the target collection signal.

[0014] Optionally, the method for determining a switch control signal based on the resonant current and the sampling time includes: determining an in-phase voltage signal corresponding to the resonant current according to the resonant current, and determining a switch control signal according to the in-phase voltage signal and the sampling time.

[0015] Optionally, the method for determining the switch control signal based on the resonant current and the sampling time includes: after the sampling time, generating a first pulse signal as a switch control signal; when the first pulse signal is at a high level, controlling the capacitor to discharge; when the first pulse signal becomes a low level, controlling the capacitor to charge.

[0016] Optionally, the target acquisition circuit is a preset peak holding circuit; the peak holding circuit is used to detect the peak voltage of the voltage absolute value signal corresponding to the current absolute value signal obtained by rectifying the resonant current through a rectifier bridge; the target acquisition signal is the peak voltage.

[0017] Optionally, the following steps are also included: after the sampling moment, according to the moment when the resonant current is equal to zero, a second pulse signal is generated; when the second pulse signal is at a high level, the peak holding circuit is controlled to be initialized so that the peak voltage maintained by the peak holding circuit becomes zero; when the second pulse signal becomes a low level, the peak holding circuit is controlled to generate a peak voltage.

[0018] Optionally, the following steps are also included: converting the resonant current into a voltage signal or a voltage absolute value signal with the same phase; comparing the voltage signal or the voltage absolute value signal with a preset voltage interval, and generating a second pulse signal if the voltage signal or the voltage absolute value signal is within the voltage interval; when the second pulse signal is at a high level, controlling the peak holding circuit to be initialized so that the peak voltage maintained by the peak holding circuit becomes zero; when the second pulse signal becomes a low level, controlling the peak holding circuit to be in an on state so that the peak holding circuit generates a peak voltage.

[0019] Optionally, the method further includes the following steps: adding a preset delay time period after the sampling time of each cycle; and sampling the target acquisition signal within or after the delay time period.

[0020] The present invention provides a control method for a high-voltage generator, which collects a target acquisition signal in a target acquisition circuit at a sampling time, and uses the collected target acquisition signal as a resonant current characteristic quantity, wherein the fluctuation of the resonant current characteristic quantity is very small, and no high-speed ADC is required. The method can be used to obtain the resonant current characteristic quantity of a fixed-frequency resonant converter, and can also be used to obtain the resonant current characteristic quantity of a variable-frequency resonant converter, and in particular, the resonant current characteristic quantity obtained in a variable-frequency resonant converter is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of a control method for a high voltage generator provided by an embodiment of the present invention.

[0022] Figure 2 It is a structural schematic diagram of a high voltage generator provided by one embodiment of the present invention.

[0023] Figure 3 This is a waveform diagram of a resonant current provided by an embodiment of the present invention.

[0024] Figure 4 It is a schematic diagram of a circuit for obtaining a resonant current characteristic quantity based on a capacitor charging and discharging circuit provided by an embodiment of the present invention.

[0025] Figure 5 Schematic diagram of a circuit of various phase shifting networks provided in one embodiment of the present invention.

[0026] Figure 6 yes Figure 4 Corresponding signal diagram.

[0027] Figure 7 It is a schematic diagram of a circuit for obtaining a resonant current characteristic quantity based on a peak holding circuit provided by an embodiment of the present invention.

[0028] Figure 8 yes Figure 7 Corresponding signal diagram.

[0029] Fig. 9 It is a schematic diagram of a circuit for obtaining a resonant current characteristic quantity based on an advanced phase-shifted voltage signal provided by an embodiment of the present invention.

[0030] Fig.10 It is a schematic diagram of a circuit for obtaining a resonant current characteristic quantity based on a capacitor charging and discharging circuit and a delay module provided by an embodiment of the present invention.

[0031] Fig.11 The present invention provides a circuit diagram for obtaining a resonant current characteristic quantity based on a peak holding circuit and a delay module according to an embodiment of the present invention.

[0032] Fig.12 A signal schematic diagram of generating a switch signal based on a preset voltage range provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, advantages and features of the present invention clearer, a control method for a high voltage generator proposed by the present invention is further described in detail below in conjunction with the accompanying drawings. It should be noted that the accompanying drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0034] In the description of the present invention, the terms "first", "second", etc. are added for the convenience of description and reference, and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined by the terms "first", "second", etc. may explicitly or implicitly include one or more of the features.

[0035] refer to Figure 1 As shown, this embodiment provides a control method for a high voltage generator, and the execution subject of the method can be Figure 2 The controller of the high voltage generator, specifically the resonant current processing module in the controller, the method comprises the following steps:

[0036] S1. Obtain the resonant current of the high-voltage generator. The resonant current of the high-voltage generator can be obtained by sampling with current measuring equipment such as an oscilloscope or current transformer. The waveform of the commonly used resonant current is referenced as follows: Figure 3 The sine wave or steamed bun wave shown. After obtaining the resonant current, the following steps can be performed directly or after filtering and noise reduction.

[0037] S2. Determine the sampling time of each cycle of the resonant current according to the resonant current. There are many methods for determining the sampling time, for example:

[0038] Method 1: Determine the sampling time of the corresponding cycle of the resonant current according to the time when the resonant current is equal to zero in each cycle of the resonant current. Figure 4-Figure 6 As shown, the resonant current is filtered out high-frequency noise to obtain the current i r , the current i r 、Current i r The corresponding in-phase voltage signal v r Or i r Sent to the phase shift network to generate a leading voltage signal v r lead The zero-crossing moment of is used as the sampling moment of the corresponding cycle of the resonant current. Figure 6 In the process, the current i r The corresponding in-phase voltage signal v r The zero-crossing moment of the current i can be used as the sampling moment of the corresponding cycle. r 、Current i r The corresponding in-phase voltage signal v r Or i r Sent to the phase shift network to generate a leading voltage signal v r_lead The time near the zero-crossing point of is used as the sampling time of the corresponding cycle of the resonant current; for example, when -a≤i r ≤a or -a≤i r The sampling time is determined when a ≤ b, and a and b represent the preset current thresholds.

[0039] Method 2: Convert the resonant current into an electrical signal whose phase is ahead of the resonant current, and determine the sampling time of the corresponding cycle of the resonant current according to the time when the electrical signal is equal to zero in each cycle of the electrical signal. Fig. 9 As shown, the current i r Send it to the phase shift network to obtain the leading voltage signal v r_lead , the leading voltage signal v r_lead The zero-crossing moment of the resonant current is used as the sampling moment of the resonant current. At the sampling moment, the MCU (Microcontroller Unit) drives the ADC (Analog-to-Digital Converter) to perform sampling. A typical advance signal is to convert the current i r Sent to the pure inductance leading network, the generated leading voltage signal v r_lead Specific current i r Leading 90 degrees, leading voltage signal v r_lead The zero-crossing time of the current ir The peak current corresponds to the moment when the current i r The current absolute value signal i obtained by rectifier bridge r_abs By sampling, the resonant current characteristic quantity close to the resonant current peak value can be obtained, and the resonant current characteristic quantity can also be called the resonant current characteristic value. In other embodiments, the leading voltage signal v r_lead The time near the zero-crossing point is used as the sampling time of the corresponding period of the resonant current.

[0040] S3. According to the sampling time of each cycle, the target acquisition circuit and the target acquisition signal in the target acquisition circuit, the target acquisition signal is sampled to obtain a resonant current characteristic value, and the resonant current characteristic value is used as an inner loop feedback value for controlling the high voltage generator. The target acquisition circuit can be in a variety of forms, and the target acquisition circuit can be Figure 4 The capacitor charging and discharging circuit shown in Figure 7 The peak hold circuit shown or Fig. 9 The target acquisition signal can have multiple forms to choose from, and the target acquisition signal can be Figure 4 The voltage V across the capacitor in the capacitor charging and discharging circuit c The maximum value V c-ht , Figure 7 The peak voltage held by the peak holding circuit or the absolute value signal of the current output by the rectifier bridge i r_abs peak value.

[0041] Optional, reference Figure 4-Figure 6 As shown, the target acquisition circuit is a preset capacitor charging and discharging circuit, and the capacitor charging and discharging circuit includes a capacitor C; one end of the capacitor C is used to input the resonant current or the current absolute value signal i obtained by rectifying the resonant current through a rectifier bridge r_abs , the other end of the capacitor C is connected to the ground; determining the switch control signal SW based on the resonant current and the sampling time on_off , according to the switch signal SW on_off Control the switch of the capacitor charging and discharging circuit to charge and discharge the capacitor C; at the sampling time, collect the maximum value V of the capacitor voltage across the capacitor C c-ht and the capacitor voltage maximum value V c-ht The capacitor charging and discharging circuit may also include a switch tube SW, a resistor R or other power-consuming elements. When the switch tube SW is disconnected, the current absolute value signal i r_abs The capacitor C is charged; when the switch tube SW is closed, the capacitor C is discharged through the resistor R or other power-consuming elements; the target acquisition signal is V at both ends of the capacitor C.c The maximum value V c-ht The switching transistor SW includes, but is not limited to, BJT (bipolar junction transistor), MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), or IGBT (Insulated Gate Bipolar Transistor).

[0042] Optionally, referring to Figure 4 and Figure 6 as shown, the method for determining the switching control signal based on the resonant current and the sampling moment includes: determining the in-phase voltage signal v corresponding to the resonant current according to the resonant current r , and determining the switching control signal SW according to the in-phase voltage signal v r and the sampling moment on_off . After determining the sampling moment according to the resonant current, the switching control signal SW can be generated after a preset time period after the sampling moment on_off .

[0043] In other embodiments, it is possible to determine the switching signal SW based on the zero-crossing moment of the leading voltage signal v generated by feeding the current i r into the phase-shifting network r_lead . The phase-shifting network can be implemented based on a series-parallel network of resistors and inductors, including but not limited to on_off several specific ways shown in Figure 5 . In addition, it is possible to perform multi-stage phase-shifting, that is, after converting the generated leading voltage signal into a current signal, passing it through the phase-shifting network again to generate a new leading voltage signal. When the MCU receives the zero-crossing signal of v r or v r_lead , it drives the ADC to sample the voltage V Figure 4 in c , and the voltage V corresponding to the current integral within half a period of the resonant current can be obtained. After the sampling is completed, the switching signal SW c_ht conducts briefly S on_off to quickly release the energy stored on the capacitor C, and after turning off S W , the capacitor C enters a new charging stage W .

[0044] Optionally, referring to Figure 4 and Figure 6 as shown, the method for determining the switching control signal based on the resonant current and the sampling moment includes: generating a first pulse signal as the switching control signal SW after the sampling momenton_off When the first pulse signal is at a high level, the switch tube SW can be controlled to be in a closed state to discharge the capacitor C; when the first pulse signal becomes a low level, the switch tube SW can be controlled to be in an open state to charge the capacitor C. The first pulse signal is the signal used by the capacitor charging and discharging circuit, that is, Figure 6 Middle switch signal SW on_off After each sampling is completed, a first pulse signal can be generated.

[0045] Optional, reference Fig.12 As shown, the method includes: converting the resonant current into a voltage signal v r Or voltage absolute value signal v r_abs ; The voltage signal v r Or the voltage absolute value signal v r_abs Compared with the preset voltage interval ref1-ref2, if the voltage signal v r Or the voltage absolute value signal v r_abs In the voltage interval ref1-ref2, a first pulse signal is generated; when the first pulse signal is at a high level, the switch tube SW is controlled to become a closed state to discharge the capacitor C; when the first pulse signal becomes a low level, the switch tube SW is controlled to become an open state to charge the capacitor C.

[0046] Optional, reference Figure 7-Figure 8 As shown, the target acquisition circuit is a preset peak holding circuit; the peak holding circuit is used to detect the current absolute value signal i obtained by rectifying the resonant current through the rectifier bridge. r_abs The corresponding voltage absolute value signal v r_abs The target acquisition signal is the peak voltage.

[0047] Optional, reference Figure 7-Figure 8 As shown, the method further includes the following steps: after the sampling time, according to the time when the resonant current is equal to zero, a second pulse signal is generated; when the second pulse signal is at a high level, the peak holding circuit is controlled to be initialized so that the peak voltage held by the peak holding circuit becomes zero; when the second pulse signal becomes a low level, the peak holding circuit is controlled to generate a peak voltage. The second pulse signal is the signal used by the peak holding circuit, that is, Figure 8 A high level signal in the peak circuit initialization signal.

[0048] Optional, reference Figure 8 and Fig.12As shown, the method further includes the following steps: converting the resonant current into a voltage signal v with the same phase r Or voltage absolute value signal v r_abs ; The voltage signal v r Or the voltage absolute value signal v r_abs Compared with the preset voltage interval ref1-ref2, if the voltage signal v r Or the voltage absolute value signal v r_abs Within the voltage range ref1-ref2, a second pulse signal is generated; when the second pulse signal is at a high level, the peak holding circuit is controlled to be initialized so that the peak voltage maintained by the peak holding circuit becomes zero; when the second pulse signal becomes a low level, the peak holding circuit is controlled to be in an on state so that the peak holding circuit generates a peak voltage.

[0049] Optional, reference Fig.10 and Fig.11 As shown, the method further includes the following steps: adding a preset delay time period after the sampling moment of each cycle; sampling the target acquisition signal within or after the delay time period. Since the delay in the actual circuit can be real, the delay time period is generated by the delay module, and the delay time period can be debugged according to the actual circuit. Within or after the delay time period, the MCU drives the ADC to sample the target acquisition signal respectively, so that the resonant current characteristic quantity obtained is more accurate and stable.

[0050] exist Figure 2In the figure, the names of the modules from left to right in the first row are input rectifier module, switch control module, resonant current module, transformer module, output rectifier filter module and tube. The input rectifier module is used to convert DC signal into AC signal, the switch control module is used to control the opening and closing frequency of the switch tube, the resonant current module is used to generate resonant current, the transformer module is used to increase the voltage, the output rectifier filter module is used to convert AC signal into DC signal and filter AC ripple, and the tube is used to generate X-rays. The main power part of the high-voltage generator based on resonant converter includes switch control module, resonant current module, transformer module and output rectifier filter module. The control process of the voltage outer loop and the resonant current inner loop is mainly as follows: the voltage at the input end of the tube is sampled to obtain a voltage sampling value; the voltage sampling value is input into the voltage processing module for screening and filtering; then an analog or digital closed-loop operation is performed with the voltage setting value corresponding to the voltage setting to obtain a voltage difference; the voltage difference is then subjected to an analog or digital closed-loop operation with the resonant current characteristic value output by the resonant current processing module to obtain a final voltage difference; the switch tube drive generation module generates a switch tube drive signal according to the final voltage difference; the switch tube drive signal drives the switch opening and closing frequency to adjust the size of the resonant current, thereby adjusting the input tube voltage.

[0051] refer to Figure 2 As shown, the control process of the voltage outer loop and the resonant current inner loop mainly includes: sampling the voltage at the input end of the bulb to obtain a voltage sampling value; the voltage sampling value is input into the voltage processing module for screening and filtering; then the voltage setting value corresponding to the voltage setting is analog or digital closed-loop operated to obtain a voltage difference; the voltage difference is directly or indirectly analog or digital closed-loop operated with the resonant current characteristic quantity output by the resonant current processing module to obtain a final voltage difference or a final current difference; the switch tube drive generation module generates a switch tube drive signal according to the final voltage difference or the final current difference; the switch tube drive signal drives the switch opening and closing frequency to adjust the size of the resonant current, thereby adjusting the voltage input to the bulb. In the process of voltage regulation, the voltage sampling value and the voltage setting value are continuously subtracted and input into the closed-loop operation, and then subtracted from the resonant current characteristic quantity to generate a switch tube drive signal, and the ultimate goal is to make the voltage sampling value equal to or close to the voltage setting value.

[0052] In summary, the present invention provides a control method for a high-voltage generator, which collects the target acquisition signal in the target acquisition circuit at the sampling time, and uses the collected target acquisition signal as the resonant current characteristic quantity, the fluctuation of the resonant current characteristic quantity is very small, and no high-speed ADC is required. This method can be used to obtain the resonant current characteristic quantity of a fixed-frequency resonant converter, and can also be used to obtain the resonant current characteristic quantity of a variable-frequency resonant converter, especially the resonant current characteristic quantity obtained in the variable-frequency resonant converter is more accurate.

[0053] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art based on the above disclosure shall fall within the protection scope of the present invention.

Claims

1. A control method for a high voltage generator, It is characterized in that The following steps are involved: Obtaining the resonant current of the high voltage generator; Determining a sampling time of each cycle of the resonant current according to the resonant current; According to the sampling time of each cycle, the target acquisition circuit and the target acquisition signal in the target acquisition circuit, the target acquisition signal is sampled to obtain a resonant current characteristic quantity, and the resonant current characteristic quantity is used as an inner loop feedback value for controlling the high voltage generator.

2. A control method for a high voltage generator as claimed in claim 1, It is characterized in that The step of determining the sampling moment of each cycle of the resonant current according to the resonant current comprises: determining the sampling moment of the corresponding cycle of the resonant current according to the moment when the resonant current is equal to zero in each cycle of the resonant current.

3. A control method for a high voltage generator as claimed in claim 1, It is characterized in that The step of determining the sampling moment of each cycle of the resonant current according to the resonant current includes: converting the resonant current into an electrical signal whose phase is ahead of the resonant current, and determining the sampling moment of the corresponding cycle of the resonant current according to the moment when the electrical signal is equal to zero in each cycle.

4. A control method for a high voltage generator as claimed in claim 1, It is characterized in that The target acquisition circuit is a preset capacitor charging and discharging circuit, and the capacitor charging and discharging circuit includes a capacitor; One end of the capacitor is used to input the resonant current, and the other end of the capacitor is connected to the ground; Determining a switch control signal based on the resonant current and the sampling time, and controlling a switch of the capacitor charging and discharging circuit according to the switch signal to charge and discharge the capacitor; At the sampling moment, the maximum value of the capacitor voltage across the capacitor is collected, and the maximum value of the capacitor voltage is used as the target collection signal.

5. A control method for a high voltage generator as claimed in claim 4, It is characterized in that The method for determining a switch control signal based on the resonant current and the sampling time includes: determining an in-phase voltage signal corresponding to the resonant current according to the resonant current, and determining a switch control signal according to the in-phase voltage signal and the sampling time.

6. A control method for a high voltage generator as claimed in claim 4 or 5, It is characterized in that The method for determining a switch control signal based on the resonant current and the sampling moment includes: after the sampling moment, generating a first pulse signal as a switch control signal; when the first pulse signal is at a high level, controlling the capacitor to discharge; and when the first pulse signal becomes a low level, controlling the capacitor to charge.

7. A control method for a high voltage generator as claimed in claim 1, It is characterized in that The target acquisition circuit is a preset peak holding circuit; the peak holding circuit is used to detect the peak voltage of the voltage absolute value signal corresponding to the current absolute value signal obtained by rectifying the resonant current through the rectifier bridge; the target acquisition signal is the peak voltage.

8. A control method for a high voltage generator as claimed in claim 7, It is characterized in that The following steps are also included: After the sampling time, generating a second pulse signal according to the time when the resonant current is equal to zero; When the second pulse signal is at a high level, the peak holding circuit is controlled to be initialized so that the peak voltage held by the peak holding circuit becomes zero; when the second pulse signal becomes a low level, the peak holding circuit is controlled to generate a peak voltage.

9. A control method for a high voltage generator as claimed in claim 7, It is characterized in that The following steps are also included: The resonant current is converted into a voltage signal or a voltage absolute value signal with the same phase; the voltage signal or the voltage absolute value signal is compared with a preset voltage interval, and if the voltage signal or the voltage absolute value signal is within the voltage interval, a second pulse signal is generated; when the second pulse signal is at a high level, the peak holding circuit is controlled to be initialized so that the peak voltage held by the peak holding circuit becomes zero; when the second pulse signal becomes a low level, the peak holding circuit is controlled to be in an on state so that the peak holding circuit generates a peak voltage.

10. A control method for a high voltage generator as claimed in claim 1, It is characterized in that The following steps are also included: A preset delay time period is added after the sampling time of each cycle; and the target acquisition signal is sampled within or after the delay time period.

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