Multi-level bus advanced prediction tracking control method for high-voltage direct-current power supply

Abstract

The invention provides a multi-level bus advanced prediction tracking control method for a high-voltage direct-current power supply. Output current information in a k period is collected in real time through a load characteristic sampling unit and enters an STM32 through an analog-to-digital conversion unit. Calculating to obtain a normal working point corresponding to a (k + 1) period, outputting a corresponding voltage control signal, and outputting a corresponding voltage control signal; and comparing with a set threshold value, if the threshold value is greater than the threshold value, the multi-level bus regulation unit performs voltage regulation and control to obtain a voltage control signal obtained by calculation and outputs the voltage control signal, and then the output voltage is regulated by enabling output voltage change information to enter a power closed loop. The output voltage is predicted in real time through the current information, and the level switching delay is reduced. According to the invention, the control mode for realizing multi-level switching is simple, and the method has good adaptability and extensibility. The condition of load abrupt change can be well responded, rapid cooperative adjustment is carried out, and the response speed and stability of the power supply system are improved.

Description

Technical Field

[0001] The present invention relates to multi-level tracking switching technology, and particularly to a multi-level bus lead prediction tracking control method for high-voltage DC power supplies. Background Art

[0002] In the field of application of power electronics technology, multi-level tracking switching technology is the key to the high efficiency and high reliability of power electronic systems, especially in the fields of new energy, smart grid, electric vehicles, etc. The core challenges it faces include dynamic response speed, avoiding voltage distortion caused by level switching delay under rapid load changes; equalization control, the problem of equalizing the capacitor voltages and the voltage and current sharing of power devices in multi-level systems; prediction accuracy, predicting the level switching timing in advance to eliminate the oscillation risk of traditional hysteresis control.

[0003] The implementation methods of multi-level tracking switching technology generally include hardware topology architecture, modulation and switching strategies, and tracking switching control logic. Among them, the topology architecture usually uses diode clamping, flying capacitor, and modular multi-level converter to achieve different level mode outputs; the modulation and switching strategies generally use carrier-based PWM, space vector modulation, and nearest level approximation; in the tracking switching control logic, hysteresis comparison control triggers level switching by real-time monitoring of the bus voltage / current when it exceeds the set threshold, which is simple but prone to oscillation; model predictive control solves the delay problem of traditional hysteresis control by establishing a system dynamic model and calculating the optimal switching timing in advance through rolling optimization; adaptive threshold adjustment dynamically corrects the switching threshold according to load changes to avoid overvoltage / undervoltage risks caused by fixed thresholds.

[0004] For the entire multi-level control power supply, it mainly includes a bus control unit and a main power conversion unit, where the main power conversion unit is usually implemented in a combination of a switching conversion unit and a resonant unit. Common resonant units can be divided into LC series resonance, LC parallel resonance, LLC resonance, LCC resonance and other combined resonance forms. For these resonant topologies, the output gain can be adjusted by changing the switching frequency of the switching conversion unit. Since the gain adjustment is limited, and in some application scenarios, the power supply needs to be able to output in a wide range according to the characteristics of the load it drives. At this time, a multi-level tracking switching power supply mode needs to be adopted to achieve the wide-range output requirement. In addition, the output characteristics vary greatly for different loads. For resistive loads, when the load changes dynamically, the current changes instantaneously, resulting in current spikes, while the voltage on the load needs time to establish, with a certain delay.

[0005] In a high-voltage DC power supply system for wide-range output, where the output voltage range is from several hundred volts to several thousand volts and stable output of wide-range voltage is required, in application scenarios, based on the topology of an adjustable-output voltage DC converter, according to the boost ratio range that the converter can achieve, the input DC bus voltage of the front stage of the converter needs to be tracked and dynamically adjusted. For example, in a multi-level bus tracking scheme, to ensure stable DC voltage output of the high-voltage DC converter. However, a scheme such as multi-level bus tracking has a control lag characteristic, that is, the bus needs to decide the output bus voltage level according to the voltage level at the output end. However, in the process from sampling the output voltage at the output end to the output of the bus switching control signal, and then to the process of establishing a new level voltage for the bus, there is a serious lag characteristic, resulting in the problem that the output voltage is clamped by the low bus level and distorted. Especially in the working condition of load step switching at the output end, the distortion problem is more prominent. Summary of the Invention

[0006] 1. Technical problems to be solved: How to improve the speed of multi-level bus tracking in this wide-range high-voltage DC power supply scenario and ensure that the system continuously outputs a stable desired DC voltage.

[0007] 2. Technical solution: To solve the above problems, the present invention provides a multi-level bus lead prediction tracking control method for a high-voltage DC power supply, based on a multi-bus switching system. The multi-bus switching system includes a multi-level bus adjustment unit, a power conversion unit, a variable load, a load characteristic sampling unit, an analog-to-digital conversion unit, an STM32, and a bus switching control unit. The control method includes the following steps: Step S01: The k output current information within a cycle I out ( k ) is collected in real time by the load characteristic sampling unit and enters the STM32 through the analog-to-digital conversion unit.

[0008] Step S02; Perform operations to obtain the normal operating point corresponding to the ([[]]END]] k +1) cycle, and output the corresponding voltage control signal U out_ref ( k +1), and output the corresponding voltage control signal U out_ref ( k +1).

[0009] Step S03: Compare the voltage control signal U out_ref ( k +1) with the set threshold. If it is greater than the threshold, perform voltage regulation through the bus switching control unit and the multi-level bus adjustment unit to becomeU out_ref ( k +1) and output it, then enter the output voltage change information into the power closed-loop to adjust the output voltage.

[0010] The specific circuit structures of the bus switching control unit and the multilevel bus regulation unit include a buck-type Buck conversion circuit, a sampling resistor switching circuit, and a numerical control circuit. k The output current information within a I out ( k ) is collected in real time and enters the STM32 for calculation to obtain the normal operating point corresponding to the ( k +1) cycle, and the corresponding voltage control signal is output U out_ref ( k +1), and it is compared with the set bus switching threshold A. When the calculated voltage signal U out_ref ( k +1) is greater than the bus switching threshold A, the Buck circuit sampling switching circuit works, and one of the sampling resistors is short-circuited, and the Buck output voltage changes accordingly. At the same time, the calculated voltage signal U out_ref ( k +1) is used as the feedback signal of the power conversion circuit for closed-loop operation to adjust the output voltage U out .

[0011] The multi-bus switching system is a double-loop control, which is divided into a bus tracking loop and a high-voltage output voltage loop. The bus tracking loop includes a digital control unit, a multilevel bus regulation unit, and a power conversion unit. The high-voltage output voltage loop includes a sampling conditioning unit, a digital control unit, and a power conversion unit.

[0012] The delay time of the bus tracking loop includes a signal acquisition delay time t a , a digital operation delay t b and a bus closed-loop regulation delay time t c , that is t 1 = t a + t b + t c .

[0013] The delay time of the high-voltage output loop mainly includes a signal acquisition delay time t a, Digital operation delay t b , Power closed-loop regulation delay time t d , t 2 = t a + t b + t d .

[0014] The delay time of the double-loop control is t delay = t 2 - t 1, the limit value of the speed matching delay time t delay_limit , This value is used to evaluate the reliability of the multi-loop matching delay.

[0015] 3. Beneficial effects: The multi-level bus advanced prediction tracking control method for high-voltage DC power supplies proposed by the present invention does not rely on real-time feedback information of the closed-loop voltage, but predicts the output voltage in real time through current information, which can greatly reduce the level switching delay and improve the dynamic response. The control method for realizing multi-level switching is simple, without the need for historical data, and the implemented hardware topology structure is simple, and has good adaptability and expandability. Through the multi-closed-loop collaborative prediction control method, it can well respond to the sudden change of the load, perform rapid collaborative adjustment, and improve the response speed and stability of the power supply system. Description of the drawings

[0016] Figure 1 is a schematic structural diagram.

[0017] Figure 2 is a schematic circuit structure diagram of the multi-bus advanced prediction tracking switching core unit.

[0018] Figure 3 is a comparison diagram of the process waveforms of different control methods, where (a) is the advanced prediction control method and the traditional control method, and (b) is the advanced prediction control method.

[0019] Figure 4 is a schematic diagram of the structure block diagram of the double-loop control and the delay time of each link.

[0020] Figure 5 is a schematic diagram of the flowchart of the double-loop control and the composition of the delay time of each link.

[0021] Figure 6 is a schematic diagram of the load characteristic curve.

[0022] Figure 7Under static load, it is the output waveform diagrams of loads with different characteristics. (a) Output voltage and current under load B condition; (b) Output voltage and current under load C condition; (c) Corresponding bus voltage level under load B condition; (d) Corresponding bus voltage level under load C condition.

[0023] Figure 8 It is a schematic diagram of the structure of the dynamic load experiment platform.

[0024] Figure 9 It is the waveform diagram of bus voltage level switching under dynamic load conditions within the same power supply voltage range.

[0025] Figure 10 It is the waveform diagram of bus voltage level switching under dynamic load conditions within different power supply voltage ranges.

[0026] Figure 11 It is the output voltage waveform diagram under the condition of a load with continuously changing characteristics. Specific implementation mode

[0027] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0028] The present invention provides a multi-level bus lead prediction and tracking control method for a high-voltage DC power supply, based on a multi-bus switching system. The multi-bus switching system includes a multi-level bus regulation unit, a power conversion unit, a variable load, a load characteristic sampling unit, an analog-to-digital conversion unit, an STM32, and a bus switching control unit. The control method includes the following steps: Step S01: k The output current information within one I out ( k ) is collected in real time by the load characteristic sampling unit and enters the STM32 through the analog-to-digital conversion unit.

[0029] Step S02: Calculate to obtain the normal operating point corresponding to the ( k + 1)th period, and output the corresponding voltage control signal U out_ref ( k + 1), and output the corresponding voltage control signal U out_ref ( k + 1).

[0030] Step S03: Compare the voltage control signal U out_ref ( k + 1) with the set threshold. If it is greater than the threshold, voltage regulation is performed through the bus switching control unit and the multi-level bus regulation unit to U out_ref (k (+1) and output it. Then, by inputting the output voltage change information into the power closed-loop, the output voltage is adjusted.

[0031] Figure 1 It is a schematic diagram of the structure of a multi-level bus dynamic switching tracking control method based on lead prediction. The entire multi-bus switching system mainly consists of a multi-level bus regulation unit, a power conversion unit, a variable load, a load characteristic sampling unit, an analog-to-digital conversion unit, an STM32, and a bus switching control unit. Among them, the STM32 digital controller, the bus switching control unit, and the multi-level bus regulation unit are the cores of the multi-level bus dynamic switching tracking control.

[0032] For a voltage source, it is generally equivalent to a large capacitor. When the load changes, the output current at this time will also change instantaneously. However, due to the fact that the capacitor voltage cannot change abruptly, the voltage change has hysteresis. At this time, k the current information that synchronously changes in the cycle I out ( k ) enters the STM32 digital controller through the load characteristic sampling unit, and through calculation, the normal operating point corresponding to the ( k +1) cycle is obtained and the corresponding voltage control signal is output U out_ref ( k +1), which is compared with the set threshold value to judge the level value of the bus switching at the current moment U bus ( k ). After that, the output voltage change information with hysteresis is then input into the power closed-loop to adjust the output voltage, thereby realizing the advance prediction of the normal operating point of the changed load through the instantaneously changing current information, and switching to the corresponding bus level in advance, so that the system output voltage can be adjusted to the corresponding output value as soon as possible, realizing real-time detection of the current and advance prediction to control the output voltage.

[0033] The present invention samples the voltage information on the output side of the high-voltage DC power supply in real time U out , and at the same time, the corresponding output current information is collected in real time I out . Since the high-voltage DC power supply expects to control the voltage at the output end within the constant power operating region, which will change in real time with the change of the output current, the control method proposed by the present invention not only considers the output voltage information at the current moment U out ( k ), where k is the current control cycle, and at the same time, the expected control reference voltage information at the output end of the next control cycle is considered U out_ref (k +1), combine the information of both to judge and determine the bus switching level value at the current moment U bus ( k ). Since the voltage at the actual high-voltage output terminal has not been adjusted and updated, while the bus voltage output has established the bus level corresponding to the new operating point, for the changing output terminal voltage, it belongs to predictive control, thus solving the problem of closed-loop distortion of the output terminal voltage caused by the lagging property of bus voltage switching.

[0034] In the present invention, it is implemented through software logic in the digital controller U out_ref ( k +1) exceeds the threshold of the preset first hysteresis unit, then the output of the bus control switching instruction is carried out. At the same time, when the digital controller gives the bus switching instruction, this instruction signal enters an additional hysteresis comparator hardware circuit unit, and is judged with the threshold of the preset second hysteresis unit, and finally the switching instruction signal is output to control the bus level value output by the bus switching unit. This dual-hysteresis bus switching control method of digital and hardware circuits effectively avoids the oscillation information on the high-voltage output side, especially the problem of misoperation of bus switching caused under the condition of load switching, and ensures the stable operation of the entire high-voltage DC power supply system.

[0035] In one embodiment, as Figure 2 shown, the specific circuit structure of the multi-bus predictive tracking switching core unit mainly consists of a buck-type Buck conversion circuit, a sampling resistor switching circuit, and a numerical control circuit, and the structure is very simple. Its main working principle is to k the output current information within the I out ( k ) is collected in real time and enters the digital controller, and through calculation, the normal operating point corresponding to the ( k +1) period is obtained, and the corresponding voltage control signal U out_ref ( k +1) is output, and compared with the set bus switching threshold A. When the calculated voltage signal U out_ref ( k +1) is greater than the bus switching threshold A, the Buck circuit sampling switching circuit works, and one of the sampling resistors is short-circuited, and the Buck output voltage changes accordingly, that is, the bus level switches. At the same time, the calculated voltage signal U out_ref ( k +1) is used as the feedback signal of the power conversion circuit for closed-loop operation to U outAdjustment is carried out to achieve the advance prediction of the normal operating point of the changed load through the changing current information, so as to switch to the corresponding bus level in advance, enabling the system output voltage to be adjusted to the corresponding output value as soon as possible, and realizing the real-time detection of current and advance prediction to control the output voltage. Vice versa. For the traditional level switching control method, it is to control the switching of the bus level by real-time detecting the output voltage and comparing it with the set switching voltage threshold.

[0036] In the design of the bus switching unit, the corresponding multi-level bus voltage output is realized based on the same DC-DC converter main power topology, the Buck main power converter topology. By switching the resistance value of the voltage sampling resistor at the output end of the Buck converter, the switching of the Buck output sampling voltage value is realized. Different sampling voltage values enter the Buck closed-loop controller unit, and finally different voltage levels are output by the Buck, completing the output requirements of different bus flat values. Compared with the traditional scheme of realizing the superposition output of multiple level values by using multiple independent isolated power modules, the present invention only uses one-level power topology, and realizes the multi-level bus output by switching the closed-loop control loop. The circuit structure is simpler, the control is more stable, and the method has strong universality and good expandability.

[0037] From Figure 3 the waveform comparison and analysis, it can be seen that compared with the traditional multi-level bus tracking and switching method, the multi-level bus dynamic switching and tracking control method with advance prediction can quickly locate the normal operating point of the sudden change load, greatly reduce the phenomena of output overcurrent and overvoltage, thereby reducing the time for the power supply system to work at abnormal operating points, and can greatly improve the level switching speed and at the same time improve the stability of the power supply system.

[0038] In one embodiment, as Figure 4 shown, the multi-bus switching system is a double-loop control, divided into a bus tracking loop and a high-voltage output voltage loop. The bus tracking loop includes a digital control unit, a multi-level bus adjustment unit and a power conversion unit. The high-voltage output voltage loop includes a sampling conditioning unit, a digital control unit and a power conversion unit. The matching delay between the two loops has an important impact on the stability of the output.

[0039] As Figure 4 and Figure 5 shown, the present invention gives the limit value of the loop speed matching delay time t delay_limit , exceeding this limit value, the double-loop working system will be in a state of system oscillation or serious waveform distortion, thus providing a guiding reference for the loop speed matching of power supply systems similar to double-loop control. The delay time of the bus tracking loop mainly includes the signal acquisition delay time t a and the digital operation delayt b and the closed-loop regulation delay time of the bus t c , that is t 1 = t a + t b + t c . The delay time of the high-voltage output loop mainly includes the signal acquisition delay time t a , digital operation delay t b , power closed-loop regulation delay time t d , t 2 = t a + t b + t d . Therefore, the delay time of the dual-loop control is t delay = t 2 - t 1. Through experiments and parameter optimization, the limit value of the loop speed matching delay time can be obtained t delay_limit , and this value can be used to evaluate the reliability of the multi-loop matching delay.

[0040] The present invention proposes a qualitative evaluation method for the speed of the dual-loop control, and the control speed of the bus tracking loop needs to be greater than the control speed of the output voltage loop. The speed matching time of the two is measured by the measured phase shift time t delay to evaluate. That is, by detecting the voltage waveform at the output end with an oscilloscope, the corresponding moment of the expected set voltage point is t 1, and the starting moment of the bus switching action is t 2, then the dual-loop speed matching delay time is t delay = t 2 - t 1. Thus, through experimental exploration, the limit value of the loop speed matching delay time t delay_limit is given. Exceeding this limit value, the dual-loop working system will be in a state of system oscillation or serious waveform distortion, thus providing a guiding reference for the loop speed matching of power supply systems with similar dual-loop control.

[0041] Conduct feasibility experimental verification, and select the load characteristic curve as Figure 6As shown, it is a linearly varying load, which linearly increases as the output current decreases. Its working region is divided into four parts. The bus output level is 1 in the A-B region, 2 in the B-C region, 3 in the C-D region, and 4 in the D-E region. The power conversion unit adopts a full-bridge LLC resonant topology and integrates a voltage closed-loop module inside. Since the gain adjustment range of LLC resonance is small and the efficiency drops significantly when deviating from the resonance point, the multi-level tracking switching method can improve the working characteristics of LLC when the load variation range is large. When the load changes dynamically, the current changes instantaneously. The digital controller collects the real-time current information and realizes the predictive control by judging its subsequent change rate.

[0042] A feasibility experiment was carried out for verification. First, it was verified that this control method can achieve the dynamic tracking and switching of the multi-level bus under a static load. An output experiment was carried out with a fixed-resistance load, and the loads B1 and C1 were respectively loaded, and the corresponding bus levels were U bus2 and U bus3 . The real output voltage, output current waveform, and bus level input waveform were measured respectively using a voltage probe and a current probe. The output waveform is as Figure 7 shown. According to the load characteristic curve, the ideal output voltages at B1 and C1 are U B1 , U C1 , the ideal output currents are I B1 , I C1 , and the ideal bus levels are U bus2 and U bus3 . It can be seen from the waveform diagram that the actual measured values are consistent with the ideal situation, and at the same time, the working bus level is also normally switched to the corresponding set bus level. Therefore, under the condition of a static load, the multi-level bus dynamic switching tracking control method with predictive control can realize the bus level switching by tracking the load characteristics.

[0043] Next, it was verified that this control method can achieve the dynamic tracking and switching of the multi-level bus under a dynamic load. When the power supply is operating normally, a high-voltage relay is used to change the output load value to create a dynamic load condition to verify the feasibility of this control method. Two series resistors, which are R 1 and R 2 respectively, are connected to the output end, and a high-voltage relay is connected to R 2 to control whether this resistor is connected to the circuit. By setting R 1 and RThe resistance value of 2 is used to obtain the dynamic switching form between different loads with the operation of the relay, that is, the load carried by the corresponding power supply is in a mutation situation. The circuit structure is as Figure 8 shown.

[0044] Test whether the dynamic load change will cause the bus to have an incorrect level switching phenomenon within the same operating level. Select two loads R B2 , R B3 , where R B2 is between R B and R B1 , and is equal to R 1 + R 2, R B3 is between R B1 and R C , and is equal to R 1. First, turn on the high-voltage relay. At this time, R 2 is short-circuited, and the output equivalent load is R B3 . The power supply starts to work normally. At this time, turn off the high-voltage relay, and the equivalent load becomes R B2 . Finally, turn on the high-voltage relay again, and the equivalent load changes back to R B3 . The test waveform is as Figure 9 shown. It can be seen that within the same bus level operating range, the dynamic change of the load will not cause an incorrect switching of the bus level, and it is always U bus2 .

[0045] Then test whether the dynamic load change can make the bus quickly and correctly follow the switching of the operating level within different operating levels. Select two loads R B1 and R C1 as the dynamic switching objects. The test waveform is as Figure 10 shown. It can be seen from the figure that when the load is quickly switched, the bus follows the switching action synchronously, and the delay time is very short. And even in the case of continuous load mutations, it can still work normally, with good stability. Through the dynamic load switching experiments within the same level and different levels, it can be confirmed that the multi-level bus dynamic switching tracking control method with lead prediction can achieve the tracking of the load characteristics to realize the bus level switching, and has good stability and rapidity.

[0046] Finally, verify that this control method can achieve dynamic tracking and switching of the multi-level bus under continuously changing load conditions. The actual load is as follows Figure 8 The variable load shown, whose equivalent load gradually increases with the power-on time. The actual measured output voltage waveform is as follows Figure 11 shown. It can be seen that as the load gradually increases, the bus level will also automatically switch accordingly, and the switching is smooth without obvious traces. Through the test experiment under continuously changing load conditions, it is also confirmed that the multi-level bus dynamic switching tracking control method based on lead prediction has practical application value and can achieve smooth switching.

Claims

1. A multi-level bus lead prediction tracking control method for a high-voltage DC power supply, characterized in that: Based on a multi-bus switching system, the multi-bus switching system includes a multi-level bus regulation unit, a power conversion unit, a variable load, a load characteristic sampling unit, an analog-to-digital conversion unit, an STM32, and a bus switching control unit. The control method includes the following steps: Step S01: Place k Output current information within a period I out ( k ) Collect it in real time through the load characteristic sampling unit and enter the STM32 through the analog-to-digital conversion unit; Step S02; perform an operation to obtain the normal operating point corresponding to the ( k +1) cycle, and output the corresponding voltage control signal U out_ref ( k +1), and output the corresponding voltage control signal U out_ref ( k +1); Step S03: The voltage control signal U out_ref ( k +1) is compared with the set threshold. If it is greater than the threshold, voltage regulation is performed through the bus switching control unit and the multilevel bus regulation unit to become U out_ref ( k +1) and output. Then, by inputting the output voltage change information into the power closed-loop, the output voltage is regulated.

2. The multi-level bus lead prediction tracking control method for a high-voltage DC power supply according to claim 1, characterized in that: The specific circuit structures of the bus switching control unit and the multilevel bus regulation unit include a buck converter circuit, a sampling resistor switching circuit, and a numerical control circuit. The k output current information within a I out ( k ) is collected in real time and enters the STM32 for calculation to obtain the normal operating point corresponding to the ( k +1) cycle, and the corresponding voltage control signal U out_ref ( k +1) is output and compared with the set bus switching threshold A. When the calculated voltage signal U out_ref ( k +1) is greater than the bus switching threshold A, the Buck circuit sampling switching circuit works, and one of the sampling resistors is short-circuited, and the Buck output voltage changes accordingly. At the same time, the calculated voltage signal U out_ref ( k +1) is used as the feedback signal of the power conversion circuit for closed-loop operation to regulate the output voltage U out .

3. The multi-level bus leading prediction tracking control method for a high-voltage DC power supply according to claim 1, characterized in that: The multi-bus switching system is a double-loop control, which is divided into a bus tracking loop and a high-voltage output voltage loop. The bus tracking loop includes a digital control unit, a multi-level bus regulation unit, and a power conversion unit. The high-voltage output voltage loop includes a sampling conditioning unit, a digital control unit, and a power conversion unit.

4. The multi-level bus lead predictive tracking control method for a high-voltage DC power supply according to claim 3, wherein: The delay time of the bus tracking loop includes the signal acquisition delay time t a , digital operation delay t b and the bus closed-loop regulation delay time t c , that is t 1 = t a + t b + t c .

5. The multi-level bus lead prediction tracking control method for a high-voltage DC power supply according to claim 4, characterized in that: The delay time of the high-voltage output loop mainly includes signal acquisition delay time t a , digital operation delay t b , power closed-loop regulation delay time t d , t 2 = t a + t b + t d .

6. The multi-level bus lead prediction tracking control method for a high-voltage DC power supply according to claim 5, characterized in that: The delay time of the double-loop control is t delay = t 2 - t 1, the limit value of the speed matching delay time t delay_limit , which is used to evaluate the reliability of the multi-loop matching delay.

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