Dummy load circuit for LLC high-voltage direct-current power supply no-load voltage stability control and control method

Abstract

The invention relates to a dummy load circuit for LLC high-voltage direct-current power supply no-load voltage stability control and a control method. Comprising a dummy load which is connected with a dummy load access circuit and is used for zero-load voltage amplitude limiting of the LLC resonant converter; the dummy load access circuit is used for dynamically connecting or disconnecting a dummy load according to the control signal of the digital control circuit; the auxiliary winding is arranged on the primary side of the transformer; the rectifying and filtering circuit is arranged between the auxiliary winding and the dummy load circuit and is used for rectifying the alternating current signal into direct current; and when the digital control circuit detects that the LLC high-voltage direct-current power supply enters the no-load state, the digital control circuit sends out a control signal to start the dummy load access circuit so as to realize the connection between the dummy load and the auxiliary winding. According to the method, the resistance value of the dummy load is accurately designed, circuits and mathematical models of dummy load resistance and LLC converter system gain are established, optimal dummy load resistance parameters are designed, and the system efficiency of the whole power supply system under the full-working-condition operation condition is further guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, in particular to a dummy load circuit and a control method for stable control of no-load voltage of an LLC high-voltage direct current power supply. Background Art

[0002] In the field of isolated DC-DC conversion technology, the LLC resonant converter, due to its unique resonant characteristics, can achieve zero voltage switching (ZVS) on the primary side and zero current switching (ZCS) on the secondary side, demonstrating excellent efficiency and power density. This topology features a wide voltage gain range, effectively coping with dynamic fluctuations in input voltage, and has therefore gained widespread application in DC power supply systems. However, under no-load conditions, due to the coupling effect of parasitic parameters, its gain curve appears to be upward, resulting in an increase in output voltage, posing a significant challenge to the system's closed-loop control and operational stability.

[0003] To address the issue of output voltage rise in LLC resonant converters under no-load conditions, key technologies include control strategy optimization, hardware innovation, and structural switching. While these approaches can improve no-load voltage stability to a certain extent, they each carry the risk of increasing system cost and design complexity, leading to increased switching losses, or compromising output voltage stability. New circuit optimization methods are needed to address these shortcomings.

[0004] In LLC resonant converter applications, unstable output voltage under no-load conditions is a key issue, closely related to the resonant cavity gain characteristic curve. As the quality factor (Q) decreases (i.e., the equivalent load resistance increases and the load decreases), the LLC resonant converter needs to increase the switching frequency to maintain the same resonant gain. However, in actual operation, increasing the switching frequency under light load conditions may actually increase the resonant gain, causing the output voltage to rise and even triggering overvoltage protection. This phenomenon is primarily due to the non-ideal characteristics of the high-frequency transformer's core and windings. Their distributed capacitance, combined with the parasitic capacitance of the synchronous rectifier, affects the circuit parameters, causing the gain characteristic to shift.

[0005] During no-load operation, resonant cavity parameter mismatch and parasitic capacitance coupling often lead to high voltage drift. While traditional pure control strategies can suppress voltage drift to a limited extent, they place stringent demands on the circuit's multi-parameter coupling sensitivity and dynamic response delay. Therefore, an equivalent power dissipation path can be constructed to force the resonant network out of the high-gain danger zone, while also avoiding the increased control complexity and increased EMI interference associated with traditional solutions.

[0006] Solutions to the high no-load voltage drift problem in LLC resonant converters are primarily categorized into two categories: control optimization and hardware improvements. In terms of control optimization, frequency modulation strategies can be improved, such as by adopting adaptive frequency control and segmented frequency modulation, to achieve precise regulation of the output voltage. In terms of hardware improvements, the common practice is to add preload or dynamic load circuits, or optimize the resonant network parameters, to effectively suppress the high voltage drift during no-load operation. Control optimization solutions offer the advantage of low cost, but are relatively complex and require in-depth theoretical analysis and precise algorithm design. Hardware improvements, on the other hand, offer stable and reliable results, but may increase the number of components and cost, necessitating a comprehensive trade-off during design. Existing technical challenges lie in three key areas: low-cost suppression of no-load voltage drift; no-load stability under a wide input voltage range; and efficiency during no-load operation.

[0007] Therefore, voltage regulation in LLC resonant converters under no-load conditions currently faces multiple challenges. These include the difficulty in precisely controlling the nonlinear relationship between switching frequency and resonant gain; the influence of distributed capacitance and parasitic parameters, which causes the gain curve to warp upward; electromagnetic interference introduced by traditional control strategies, which affects system stability; and the potential harm of excessive output voltage ripple to load devices. To address these issues, a new circuit optimization method is needed to suppress voltage rise while optimizing system efficiency and control accuracy, thereby achieving stable operation of the LLC resonant converter over a wide load range. Summary of the Invention

[0008] The present invention aims to provide a dummy load circuit and a control method for stabilizing the no-load voltage of an LLC high-voltage direct current power supply.

[0009] The technical solution adopted by the present invention to achieve the above-mentioned object is: a dummy load circuit for no-load voltage stabilization control of an LLC high-voltage DC power supply, comprising:

[0010] A dummy load is connected to the dummy load access circuit and is used for limiting the no-load voltage of the LLC resonant converter;

[0011] A dummy load is connected to the circuit, and the dummy load is dynamically connected or disconnected according to the control signal of the digital control circuit;

[0012] Auxiliary winding, located on the primary side of the transformer;

[0013] The rectifier filter circuit is provided between the auxiliary winding and the dummy load circuit and is used to rectify the AC signal into DC;

[0014] The digital control circuit sends a control signal to turn on the dummy load access circuit when detecting that the LLC high-voltage DC power supply enters a no-load state, so as to achieve connection between the dummy load and the auxiliary winding.

[0015] When no-load, the parallel equivalent impedance R of the no-load value and the dummy load value of the transformer main winding of the LLC resonant converter is ac,total as follows:

[0016]

[0017] Dummy load R dummy_load Connected to the auxiliary winding, the impedance reflected to the primary side is n 2 R dummy_load , where n is the turns ratio of the auxiliary winding to the main winding (i.e., the primary winding), R L is the load on the secondary winding.

[0018] The resistance of the dummy load meets the following conditions:

[0019]

[0020] Among them, M dc is the desired target gain, f n is the normalized frequency, L n is the normalized inductance value, and n is the turns ratio of the auxiliary winding to the main winding, i.e., the primary winding.

[0021] The dummy load access circuit includes a transistor, a diode and a resistor;

[0022] The drain of the transistor is connected to the dummy load via the resistor R1, and the node between the resistor R1 and the dummy load serves as the first input terminal of the dummy load access circuit; the source of the transistor is connected to the ground;

[0023] The gate of the transistor is connected to the digital control circuit, the gate is grounded through a parallel diode and resistor R2, and is connected to the second input terminal of the circuit as a dummy load;

[0024] The first input terminal and the second input terminal of the dummy load access circuit are connected to the rectifier and filter circuit.

[0025] The dummy load control method for no-load voltage stabilization control of an LLC high-voltage direct current power supply comprises the following steps:

[0026] When the digital control circuit LLC high voltage DC power supply enters the no-load state, it sends a control signal to start the dummy load access circuit;

[0027] The dummy load access circuit dynamically accesses the dummy load according to the control signal of the digital control circuit, so that the dummy load is connected to the auxiliary winding of the primary side of the transformer provided in the LLC resonant converter through the dummy load access circuit and the rectifier and filter circuit, so as to realize the no-load voltage limiting of the LLC resonant converter.

[0028] The dummy load connection circuit dynamically connects the dummy load according to the control signal of the digital control circuit. The digital control circuit gives a transistor control signal to determine the working condition of the dummy load connection:

[0029] When the digital control circuit detects that the LLC high-voltage DC power supply enters the no-load state, that is, the current on the high-voltage power output side is less than the set value, the output signal turns on the transistor, and the dummy load is connected to the main circuit;

[0030] When shutting down, the dummy load is disconnected.

[0031] The present invention has the following beneficial effects and advantages:

[0032] (1) The present invention designs an additional auxiliary winding on the LLC transformer. After rectifying the AC voltage coupled from the auxiliary winding, a dummy load resistor is added. This allows the LLC converter transformer to still have a certain amount of energy transmission even when the high-voltage output winding is disconnected from the load. The operating point of the LLC topology is clamped to a minimum operating point to ensure loop stability, thereby achieving a stable operating characteristic of the output characteristics of the actual equipment under test, from no-load to full range.

[0033] (2) At the same time, the present invention adds a switching switch MOSFET to the proposed dummy load branch to switch the switching status of the dummy load resistor. When the high-voltage output end is in the rated operating state, the dummy load branch is disconnected from the auxiliary winding circuit to avoid unnecessary losses in normal conditions. Only under extremely light load or no-load operating conditions, the dummy load is switched to the auxiliary branch to ensure stable closed-loop operation of the output voltage of the high-voltage DC power supply, thereby ensuring the high efficiency characteristics of the entire LLC high-voltage DC power supply to a certain extent.

[0034] (3) The present invention designs an equivalent impedance R ac,total To achieve a reasonable design of the number of auxiliary winding turns, the turns ratio of the auxiliary winding (to the turns ratio of the main winding) will affect the impedance reflected by the dummy load to the primary side, thereby affecting the quality factor and DC gain of the LLC resonant converter, and ultimately affecting the stability and regulation capability of the output voltage. By cutting in the dummy load resistor at low voltage, the resistor selection only needs to ensure the power level parameters, without the need to consider the withstand voltage parameters of the dummy load resistor. This avoids the breakdown risk of directly connecting a resistor in parallel on the high-voltage output side, ensuring the reliability of the normal operation of the high-voltage DC power supply system.

[0035] (4) The present invention accurately designs the resistance value of the dummy load, establishes a circuit and mathematical model of the dummy load resistance and the LLC converter system gain, and designs the optimal dummy load resistance parameters, thereby further ensuring the system efficiency of the entire power supply system under full operating conditions;

[0036] (5) When the LLC high-voltage DC power supply is in normal stable operation and the dummy load resistor is cut off, the added auxiliary winding and rectifier circuit are used to perform closed-loop voltage regulation control to generate a separate auxiliary source power distribution to power the controller circuit, drive circuit, screen display circuit, etc. of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Block diagram of the LLC no-load voltage limiting dummy load circuit scheme;

[0038] Figure 2 Transformer winding circuit diagram;

[0039] Figure 3 Dummy load access circuit diagram;

[0040] Figure 4 Digital control circuit control logic flow chart;

[0041] Figure 5 DC gain curve when the quality factor is 0;

[0042] Figure 6 Circuit diagram of auxiliary source power distribution circuit;

[0043] Figure 7 LLC high-voltage DC power supply system no-load operation waveform comparison chart;

[0044] Figure 8 Complete waveform diagram of the LLC high-voltage DC power supply characteristic curve test. DETAILED DESCRIPTION

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0046] The present invention relates to the field of LLC resonant converter control technology, and is primarily used to address the problem of unstable output voltage closed loop under no-load conditions when the LLC resonant converter outputs high-voltage DC closed-loop output. To address this issue, the present invention proposes a dummy load circuit for LLC no-load voltage stabilization control:

[0047] (1) The present invention designs an additional auxiliary winding on the LLC main power transformer. After rectifying the AC voltage coupled from the auxiliary winding, a dummy load resistor is added to ensure that the transformer of the LLC converter still has a certain amount of energy transmission even when the high-voltage output winding is disconnected from the load. The operating point of the LLC topology is clamped to a lightest operating point to ensure loop stability, thereby realizing the real power output port of the power supply, connecting to the output characteristics of the equipment under test, and maintaining stable operating characteristics in the full range from no-load to satisfied.

[0048] (2) At the same time, the present invention adds a switching switch MOSFET to the proposed dummy load branch to switch the switching status of the dummy load resistor. When the high-voltage output end is in the rated operating state, the dummy load branch is disconnected from the auxiliary winding circuit to avoid unnecessary losses in normal conditions. Only under extremely light load or no-load operating conditions, the dummy load is switched to the auxiliary branch to ensure stable closed-loop operation of the output voltage of the high-voltage DC power supply, thereby ensuring the high efficiency characteristics of the entire LLC high-voltage DC power supply to a certain extent.

[0049] (3) The present invention reasonably designs the number of turns of the auxiliary winding and cuts in the dummy load resistor in a low-voltage manner. The selection of the resistor only needs to ensure the power level parameter without additional consideration of the withstand voltage parameter of the dummy load resistor, thereby avoiding the breakdown risk of directly connecting the resistor in parallel on the high-voltage output side and ensuring the reliability of the normal operation of the high-voltage DC power supply system.

[0050] (4) The present invention accurately designs the resistance value of the dummy load, establishes a circuit and mathematical model of the dummy load resistance and the LLC converter system gain, and designs the optimal dummy load resistance parameters, thereby further ensuring the system efficiency of the entire power supply system under full operating conditions;

[0051] (5) An auxiliary source power distribution design for the auxiliary winding circuit is proposed, that is, when the LLC high-voltage DC power supply is in normal stable operation and the dummy load resistor is cut off, the added auxiliary winding and rectifier circuit are used for closed-loop voltage regulation control to generate a separate auxiliary source power distribution to power the controller circuit, drive circuit, screen display circuit, etc. of the entire system. In this way, the auxiliary source power distribution design or power supply module under the power-on and power-off conditions only needs to select a smaller power level to ensure that the control circuit is powered during the startup process. After the entire LLC is running, the auxiliary source power distribution circuit of the auxiliary winding provides continuous power supply energy for the control circuit, further improving the efficiency of the system operation.

[0052] Example:

[0053] 1. Functional block diagram of LLC no-load voltage stabilization control method

[0054] The LLC no-load voltage limiting dummy load circuit proposed in this invention aims to introduce an auxiliary winding into the LLC transformer, connect a dummy load through the auxiliary winding and the rectifier filter circuit, and suppress the voltage drift problem. The solution mainly includes a dummy load, a dummy load connection circuit, a transformer auxiliary winding, an auxiliary source power distribution circuit, a rectifier filter circuit, and a digital control circuit. Figure 1 shown.

[0055] An auxiliary winding is added to the LLC resonant converter's transformer. A rectifier and filter circuit rectifies the AC signal into DC. This DC signal is then connected to a dummy load connection circuit, which dynamically connects and disconnects the dummy load based on a control signal. When the digital control circuit detects that the system is no-load, it activates the dummy load connection circuit and connects the dummy load to the auxiliary winding. This effectively suppresses voltage drift when a dummy load is connected under no-load conditions. The auxiliary power distribution circuit acts as an independent low-power supply, providing power to the control chip.

[0056] 2. Auxiliary winding type dummy load voltage stabilization circuit and working principle

[0057] The present invention proposes a solution for controlling LLC no-load voltage by adding a dummy load to the auxiliary winding. Figure 2 As shown, in a switching power supply, a high-frequency transformer is a core component and includes multiple windings. The auxiliary winding generally has fewer turns, less voltage, and less current than the secondary winding. The present invention focuses on effectively solving the problem of high voltage drift when the LLC is running at no load by adding an additional set of auxiliary windings to the main transformer and adding a dummy load to the output port of the auxiliary winding. Adding a dummy load to the auxiliary winding can effectively improve the system efficiency compared to the secondary winding. The auxiliary winding has a smaller power and the power consumption required to apply the dummy load is low. It can also simplify the circuit design without adding an additional load circuit on the secondary winding side.

[0058] A rectifier and filter circuit is also designed between the auxiliary winding and the dummy load circuit. This circuit, consisting of a fast-recovery diode and a filter capacitor, implements full-wave rectification to ensure the design of the auxiliary power distribution circuit and the DC operating point of the dummy load resistor. Compared to half-wave rectification, full-wave rectification significantly improves efficiency and has a relatively low ripple factor. Compared to bridge rectification, while retaining the advantages of symmetrical windings, the use of fast-recovery diodes and RC snubber circuits improves conducted interference suppression and reduces component costs. Compared to synchronous rectification, it eliminates complex control circuitry and improves system reliability. Through a symmetrical circuit design, full-wave rectification achieves unidirectional conduction in both the positive and negative half-cycles of the AC power, converting the AC power into pulsating DC power and optimizing the dummy load regulation.

[0059] 3. Design of control logic of dummy load unit switching circuit unit

[0060] Among them, the dummy load resistor is controlled through the dummy load access circuit, and the access circuit controls the on and off of the dummy load through MOSFET. The digital control circuit gives the MOSFET control signal to decide the working condition of the dummy load. When the digital control circuit detects that the system enters the no-load state (that is, the current on the high-voltage power output side is less than a certain value), it outputs a signal to turn on the MOSFET, and the dummy load is connected to the main circuit; when it is turned off, the dummy load is disconnected and does not affect the main circuit. The parallel diode is used to suppress the high-voltage spikes that may be generated during the switching process, protect the MOSFET and the entire circuit, and improve the reliability of the system. This dummy load access circuit has the advantages of strong controllability, high safety, and strong flexibility. The load is accurately switched by digitally controlling the MOSFET, which is suitable for adaptive dynamic adjustment; the diode provides overvoltage protection to improve system reliability. When the system leaves the no-load condition, the MOSFET is turned off to reduce power consumption, prevent inrush current and high-voltage shocks, and improve equipment stability and service life. Such as Figure 3 shown.

[0061] The digital control circuit control logic implements the scheme of dynamically adding a dummy load to the auxiliary winding for LLC no-load voltage limiting. The control logic function flow chart is as follows: Figure 4 As shown in the figure, the digital control circuit includes an analog-to-digital converter and a digital controller. The output voltage sampling circuit converts the sampled system output voltage value into a digital quantity via the analog-to-digital converter and transmits it to the digital controller. The digital controller calculates the digital quantity as the actual value and compares it with the expected no-load voltage value. If the actual value is greater than the expected value, the system will open the dummy load interface and activate the dummy load connection circuit. This digital control logic ensures the accuracy and reliability of the voltage monitoring system. By converting the sampled value into a digital quantity and performing calculations and comparisons, voltage changes can be monitored in real time and the dummy load connection status can be adjusted promptly to ensure stable system operation.

[0062] 4. Establishment of dummy load resistor parameter optimization design model

[0063] This invention proposes a dummy load circuit for LLC no-load voltage limiting. The core principle is to connect a dummy load to the auxiliary winding of the transformer to change the DC gain of the converter to achieve the purpose of controlling the output voltage. Specifically, this invention focuses on the no-load characteristics of the LLC resonant converter. After deriving the equivalent model of the LLC resonant converter according to the fundamental wave analysis method, the voltage gain M of the resonant network can be obtained. ac :

[0064]

[0065] R p is the parasitic resistance of the primary side of the transformer, L m is the magnetizing inductance, C r is the resonant capacitor, Lr is the resonant inductor, R ac is the equivalent resistance.

[0066] The characteristic impedance of the resonant network is Z o , the quality factor of the resonant network is Q, and the per-unit value of the inductor is defined as L n , the per-unit value of frequency is f n , and because R p The voltage across the two ends is n times the effective value of the secondary voltage, so:

[0067]

[0068] is the effective value of the voltage across the resonant inductor, is the effective value of the AC voltage on the input side, V b is the voltage across the resonant capacitor, V in is the input voltage, V o is the output voltage.

[0069] Arrange and normalize the above formula to get the DC gain M of the resonant circuit. dc (f n ,L n ,Q):

[0070]

[0071] When the LLC resonant converter is not loaded, it can be considered that the load impedance tends to infinity, which is equivalent to the impedance on the primary side being infinite. At this time, the quality factor Q of the resonant cavity tends to zero, and the DC voltage gain of the LLC resonant circuit becomes:

[0072]

[0073] Depend on Figure 5 It can be seen that when the quality factor is 0, as L n Increasing the DC gain value shifts the peak gain to the left and increases dramatically, which can cause problems with controlling voltage stability. Maintaining voltage stability when the DC gain is greater than 1 requires increasing the switching frequency so that it gradually approaches the resonant frequency of a gain of 1. However, rapidly changing DC gain can lead to poor system stability. When the DC gain is less than 1, the gain curve tends to a constant value, making the output voltage unadjustable.

[0074] When no-load, the equivalent impedance R ac,total It is the parallel equivalent of the no-load value and the dummy load value of the main winding. dummy_load Connected to the auxiliary winding, the impedance reflected to the primary side is n 2 R dummy_load , where n is the transformer turns ratio. Therefore, Rac,total It can be expressed as:

[0075]

[0076] But due to the main load R L It is maximum when no-load, and can be approximately considered as:

[0077] R ac,total ≈n 2 R dummy_load (6)

[0078] At this time, the quality factor Q and R ac Inversely proportional, that is:

[0079]

[0080] According to the DC gain formula of the LLC resonant converter, when the quality factor Q is not zero, the DC gain M can be expressed as:

[0081]

[0082] Combine Q and R ac Substituting the relationship into , we get:

[0083]

[0084] Since R ac ≈n 2 R dummy_load , substituting into the above formula we get:

[0085]

[0086] In order to adjust the output voltage as needed, it is necessary to adjust the dummy load resistor R at a given operating frequency f. dummy_load The gain M of the converter reaches the required value. Therefore, the optimization model of the dummy load resistor parameter can be expressed as:

[0087]

[0088] Among them, M dc is the desired target gain, f n is the normalized frequency, L n is the normalized inductance value, and n is the transformer turns ratio. Through the above model, the dummy load resistor R can be optimized according to the frequency and gain requirements in actual applications. dummy_load The value of can be selected to achieve effective regulation of the output voltage of the LLC resonant converter when it is no-load.

[0089] In the present invention, a dummy load R is connected to the auxiliary winding. dummy_load , which can significantly reduce R ac,total, thereby increasing the Q value. The gain peak shifts to the right and the peak gain decreases, increasing the frequency at which the gain requirement is achieved. Thus, at a given operating frequency, the converter gain is adjusted to the desired value, allowing the output voltage to be adjusted as needed.

[0090] 5. Design of auxiliary power distribution circuit under normal operation of auxiliary winding

[0091] The present invention proposes an auxiliary source power distribution circuit, which is composed of a transformer auxiliary winding, a rectifier filter circuit and a voltage stabilization module. The transformer auxiliary winding converts the input AC voltage into an AC low voltage suitable for subsequent circuit processing, providing preliminary power conversion for the entire distribution circuit; the rectifier filter circuit rectifies and filters the AC low voltage from the transformer, converting it into a smoother DC voltage, effectively removing ripple interference and improving power quality; the voltage stabilization module further accurately adjusts and stably controls the DC voltage after rectification and filtering, ensuring that the output voltage is not affected by input voltage fluctuations and load changes, thereby providing a stable and reliable DC power supply for electrical equipment to meet its normal power requirements. Figure 6 shown.

[0092] 6. Feasibility Verification of LLC High-Voltage DC Power Supply Open-Circuit Voltage Stability Control Scheme

[0093] The designed dummy load circuit solution is applied to the LLC high voltage DC power supply system to test whether the dummy load circuit can successfully limit the voltage under no-load conditions. First, the voltage test is carried out during the no-load operation of the LLC high voltage DC power supply system without adding a dummy load, such as Figure 7 shown.

[0094] The waveform clearly shows that, without adding a dummy load, the LLC high-voltage DC power supply achieves an output voltage of 3.979 kV at a fixed input voltage of 100 V. This exceeds the expected 2.85 kV and could damage subsequent load devices or affect system stability.

[0095] In the following test, a dummy load was introduced into the circuit and the input voltage of the power supply was kept fixed at 100V. The detailed performance verification was performed as follows: Figure 7 The test waveforms shown in Figures (a) and (b) demonstrate that the output voltage of the LLC resonant converter significantly improves after the auxiliary winding dummy load circuit is introduced, stabilizing at 2.846 kV. Compared to 3.979 kV without the dummy load, the output voltage is effectively controlled and close to the desired voltage. The addition of the dummy load significantly reduces the output voltage from 3.979 kV to 2.846 kV, ensuring output voltage stability under no-load conditions, fully meeting design expectations.

[0096] 7. Test experiment on the impact of adding the proposed dummy load network on the full range of LLC working conditions

[0097] In order to test whether the added auxiliary winding dummy load voltage stabilization scheme will affect the normal power characteristic curve output of the LLC high-voltage DC power supply, the full-range output operating point of the entire high-voltage power supply is tested. The designed dummy load circuit scheme is applied to the LLC high-voltage DC power supply system in the ion pump discharge application. The full-range operating point of the LLC high-voltage DC power supply is divided into a constant voltage operating point area, a constant power operating point area and a constant current operating point area, which is used to test whether the proposed auxiliary winding dummy load circuit will affect the stability of the power supply in the three working areas under the driving ion pump discharge condition. The test experimental waveform of the full-range operating point area during the vacuum pumping process is as follows Figure 8 shown.

[0098] Depend on Figure 8 It can be seen that the characteristic curve of the LLC high-voltage DC power supply tests the complete waveform, including the constant current region, constant power region, and constant voltage region. After adding the auxiliary winding dummy load to the LLC power supply, there is no effect on the overall voltage stability. As can be seen from the characteristic curve, the LLC power supply has good dynamic performance and stability under different load conditions, and can maintain a stable output in the constant current region, constant power region, and constant voltage region. The added auxiliary winding dummy load circuit and control unit will not affect the normal functional output of the LLC high-voltage DC power supply. In addition, by rationally designing the auxiliary winding dummy load and closed-loop controller, not only is precise control of the output voltage achieved, but energy utilization is also improved. The auxiliary winding obtains energy from the main transformer and provides power to the controller after rectification and filtering. This process effectively utilizes energy and reduces waste.

[0099] Compared with the prior art, the present invention has the following advantages:

[0100] 1. Compared with the existing technology, the present invention reduces hardware complexity and development costs while ensuring high performance. It is particularly suitable for cost-sensitive application scenarios and provides an efficient, reliable and economical solution for the no-load voltage limiting of LLC resonant converters.

[0101] 2. The present invention has the characteristics of strong controllability, high safety and strong flexibility. It can dynamically adjust the load access according to the system status, and at the same time improve the system reliability through the overvoltage protection function of the diode.

[0102] 3. This invention solves the problem of transient fluctuations introduced by the switching process in the prior art. The dummy load access circuit structure of the present invention is simple, does not require complex frequency adjustment logic or high-precision current detection, and improves system reliability through the overvoltage protection function of the diode.

[0103] 4. Compared with the traditional solution of adding a dummy load on the output side, the dummy load access circuit for LLC no-load voltage limiting proposed in the present invention has significant advantages. When the traditional solution adds a dummy load on the output side, the dummy load needs to continuously consume electrical energy, reducing the overall efficiency of the system. The present invention dynamically controls the access of the dummy load and accesses the dummy load when the auxiliary winding side is no-load, thereby avoiding continuous energy loss and significantly improving the energy utilization efficiency of the system. The dummy load access circuit unit of the present invention suppresses the high-voltage spikes during the MOSFET switching process through a parallel diode, protecting the MOSFET and the entire circuit, while avoiding interference with the output voltage through dynamic control, further improving the reliability and safety of the system.

Claims

1. A dummy load circuit for no-load voltage stabilization control of LLC high-voltage DC power supply, characterized in that: include: a dummy load connected to the dummy load access circuit; A dummy load is connected to the circuit, and the dummy load is dynamically connected or disconnected according to the control signal of the digital control circuit; Auxiliary winding, located on the primary side of the transformer; The rectifier filter circuit is provided between the auxiliary winding and the dummy load circuit and is used to rectify the AC signal into DC; The digital control circuit sends a control signal to turn on the dummy load access circuit when detecting that the LLC high-voltage DC power supply enters a no-load state, so as to achieve connection between the dummy load and the auxiliary winding.

2. The dummy load circuit for no-load voltage stabilization control of LLC high-voltage DC power supply according to claim 1, characterized in that: When no-load, the parallel equivalent impedance R of the no-load value and the dummy load value of the transformer main winding of the LLC resonant converter is ac,total as follows: Dummy load R dummy_load Connected to the auxiliary winding, the impedance reflected to the primary side is n 2 R dummy_load , where n is the turns ratio of the auxiliary winding to the main winding (i.e., the primary winding), R L is the load on the secondary winding.

3. The dummy load circuit for no-load voltage stabilization control of LLC high-voltage DC power supply according to claim 1, characterized in that: The resistance of the dummy load meets the following conditions: Among them, M dc is the desired target gain, f n is the normalized frequency, L n is the normalized inductance value, and n is the turns ratio of the auxiliary winding to the main winding, i.e., the primary winding.

4. The dummy load circuit for no-load voltage stabilization control of LLC high-voltage DC power supply according to claim 1, characterized in that: The dummy load access circuit includes a transistor, a diode and a resistor; The drain of the transistor is connected to the dummy load via the resistor R1, and the node between the resistor R1 and the dummy load serves as the first input terminal of the dummy load access circuit; the source of the transistor is connected to the ground; The gate of the transistor is connected to the digital control circuit, the gate is grounded through a parallel diode and resistor R2, and is connected to the second input terminal of the circuit as a dummy load; The first input terminal and the second input terminal of the dummy load access circuit are connected to the rectifier and filter circuit.

5. A dummy load circuit control method for LLC high voltage DC power supply no-load voltage stabilization control, characterized in that: The following steps are involved: When the digital control circuit LLC high voltage DC power supply enters the no-load state, it sends a control signal to start the dummy load access circuit; The dummy load access circuit dynamically accesses the dummy load according to the control signal of the digital control circuit, so that the dummy load is connected to the auxiliary winding of the primary side of the transformer provided in the LLC resonant converter through the dummy load access circuit and the rectifier and filter circuit, so as to realize the no-load voltage limiting of the LLC resonant converter.

6. The dummy load circuit control method for no-load voltage stabilization control of LLC high-voltage direct current power supply according to claim 5, characterized in that: The dummy load connection circuit dynamically connects the dummy load according to the control signal of the digital control circuit. The digital control circuit gives a transistor control signal to determine the working condition of the dummy load connection: When the digital control circuit detects that the LLC high-voltage DC power supply enters the no-load state, that is, the current on the high-voltage power output side is less than the set value, the output signal turns on the transistor, and the dummy load is connected to the main circuit; When shutting down, the dummy load is disconnected.

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