A transient voltage fluctuation suppression device and method for a DC bus

Abstract

The present invention provides a device and method for suppressing transient voltage fluctuations in a DC bus. The device for suppressing transient voltage fluctuations is connected in parallel to the DC bus and includes: a main power circuit, a measuring circuit, a control circuit, and a drive circuit; the measuring circuit measures the transient current of the DC bus and the compensation current generated by the main power circuit at the current moment; the control circuit obtains a switching signal based on the transient current and the compensation current; the drive circuit sends the switching signal to the main power circuit; the main power circuit includes a transfer branch and a discharge branch; the transfer branch controls the power switch device to generate the compensation current at the next moment to compensate for the transient current of the DC bus; the discharge branch controls the mechanical switch to release the energy absorbed by the capacitor through the resistor. This solves the problem of large DC bus voltage fluctuations and large capacitor usage during the shutdown period of the accelerating electrode power supply. This reduces the transient voltage fluctuations of the accelerating electrode power supply, reduces the amount of capacitor used, and increases the reliability of the power supply system.

Description

Technical Field

[0001] The present invention belongs to the field of electronic power technology, and in particular relates to a device and method for suppressing transient voltage fluctuations of a DC bus. Background Art

[0002] The accelerating pole power supply (AGPS) of the Fusion Engineering Test Reactor's Negative Ion Neutral Beam Injector (NBI) prototype is a high-voltage power supply rated at -200kV / 25A. Because load ignition conditions often occur unpredictably, the AGPS's rectifier and inverter must be quickly shut down upon detection to prevent further energy injection into the load. Because the inverter shuts down much faster than the thyristor rectifier, the DC bus absorbs energy from the rectifier's active state, causing a sudden increase in the DC bus voltage. This places increased voltage stress on the switching devices in the power supply, potentially causing them to break down and lead to serious failure. Therefore, transient fluctuations in the DC bus voltage must be limited.

[0003] To reduce transient fluctuations in the DC bus voltage, a large number of capacitors are used on the DC bus. These capacitors reduce the power density and reliability of the power supply. In addition, if a DC bus short circuit or a bridge arm direct fault occurs, the large amount of capacitors will generate a surge current of several hundred kiloamperes, which exceeds the existing fault protection capabilities and the tolerance level of the accelerating electrode power supply, resulting in serious failure consequences.

[0004] Regarding the suppression of DC voltage fluctuations, there are currently related inventions of DC active filters that can be used to compensate for steady-state ripple in the output voltage. However, these inventions are based on steady-state operating conditions and are unable to absorb the energy of transient currents from the DC bus to suppress the transient voltage fluctuations caused by these transient currents on the DC bus voltage. Currently, most active filters are used in AC power grids to absorb harmonic currents in the power grid, but their application in DC systems is significantly less. Therefore, the existing technology has technical problems such as the inability to effectively suppress transient voltage fluctuations in the DC bus and the large amount of capacitors used. Summary of the Invention

[0005] To address the shortcomings of existing technologies and the need for improvement, this paper proposes a device and method for suppressing transient voltage fluctuations in a DC bus. This method aims to address the technical issues of large DC bus voltage fluctuations and excessive capacitor usage caused by differences in converter turn-off times. This method utilizes a fast-response model predictive control method to enable rapid and accurate tracking and compensation of transient currents in DC bus capacitors within the device.

[0006] To achieve the above objectives, according to one aspect of the present invention, a device for suppressing transient voltage fluctuations of a DC bus is provided. The device is connected in parallel to the DC bus and comprises: a main power circuit, a measurement circuit, a control circuit, and a drive circuit;

[0007] The measuring circuit is used to determine the generation time of the DC bus transient current and measure the transient current at the current time and the compensation current generated by the main power circuit;

[0008] The control circuit obtains a switching signal according to the transient current and the compensation current;

[0009] The driving circuit is connected to the main power circuit and sends the switching signal to the main power circuit;

[0010] The main power circuit includes a transfer branch consisting of a power switching device and a capacitor, and a discharge branch consisting of a mechanical switch and a resistor. The discharge branch is connected in parallel to both ends of the capacitor. The transfer branch is used to control the state of the power switching device according to the switching signal, so that the capacitor absorbs the transient current and generates a compensation current at the next moment to compensate for the transient voltage fluctuation caused by the transient current. The discharge branch is used to control the closing of the mechanical switch according to the switching signal, so as to release the energy absorbed by the capacitor through the resistor.

[0011] Optionally, the main power circuit includes two transfer branches, two discharge branches and one inductor, each of the transfer branches includes one power half-bridge and one capacitor, and each of the discharge branches includes one mechanical switch and one resistor;

[0012] A first mechanical switch and a first resistor are connected in series and then connected in parallel across a first capacitor. The two ends of the first capacitor are respectively connected to an upper end and a lower end of a first power half-bridge. The midpoint of the first power half-bridge is connected to a first end of the inductor. The second end of the inductor is connected to a positive electrode of a DC bus. The lower end of the first power half-bridge is connected to a midpoint of a second power half-bridge.

[0013] A second mechanical switch and a second resistor are connected in series and then connected in parallel across a second capacitor, wherein the two ends of the second capacitor are respectively connected to an upper end and a lower end of a second power half-bridge, and the lower end of the second power half-bridge is connected to the negative electrode of the DC bus;

[0014] Each power half-bridge is composed of two power switching devices, and the power switching devices in each power half-bridge are turned on or off in a complementary manner.

[0015] Optionally, the power switching device includes a diode;

[0016] When the DC bus operates normally, the power switching devices and the mechanical switches are all turned off, and the capacitor of each power half-bridge is charged from the DC bus through the diode.

[0017] Optionally, the capacitor C n The value range of is:

[0018]

[0019] Among them, V Cm is the maximum value allowed for the capacitor voltage, n is 1 or 2, E off It is the energy during the duration of the transient current, and the calculation formula is:

[0020]

[0021] The resistor R n The value range of is:

[0022]

[0023] Among them, t rs is the period of transient current that the transient voltage fluctuation suppression device needs to compensate, t off is the duration of the transient current to be compensated, and n is 1 or 2;

[0024] The resistor R n The power P that needs to be met Rn for:

[0025]

[0026] In a second aspect, the present invention further provides a method for suppressing transient voltage fluctuations of a DC bus, which is applied to any device for suppressing transient voltage fluctuations of a DC bus described in the first aspect, comprising:

[0027] The measuring circuit determines the generation time of the DC bus transient current and measures the transient current at the current moment and the compensation current generated by the main power circuit;

[0028] The control circuit obtains the transient current and the compensation current, and determines a switching signal according to a model predictive control algorithm;

[0029] The driving circuit sends the switching signal to the main power circuit;

[0030] The main power circuit controls the state of the power switching device of the transfer branch according to the switching signal, so that the capacitor absorbs the transient current and generates a compensation current at the next moment to compensate for the transient voltage fluctuation caused by the transient current; the main power circuit controls the closing of the mechanical switch of the discharge branch according to the switching signal, and releases the energy absorbed by the capacitor of the transfer branch through the resistor.

[0031] Optionally, the measurement circuit measures the current of the rectifier of the DC bus at a current moment and determines it as the transient current;

[0032] The measurement circuit measures the current generated by the transfer branch on the inductor L at the current moment and determines it as the compensation current.

[0033] Optionally, the control circuit acquires the transient current and the compensation current, and determines the switching signal through a model predictive control algorithm, including:

[0034] When the measurement circuit detects that the DC bus generates transient current, the control circuit traverses all possible combinations of the switching function in one sampling cycle and predicts the i of the next sampling cycle. L (k+1) and V Cn (k+1);

[0035] Calculate the cost function of each predicted compensation current and select the switching signal corresponding to the minimum cost function value as the target switching signal;

[0036] If the current generated by the transfer branch on the inductor L at the current moment is measured to be i L (k), then the compensation current i at the next moment is determined according to the model predictive control algorithm L (k+1) is:

[0037]

[0038] Capacitor voltage V Cn (k+1) is:

[0039]

[0040] Among them, i L (k) is the compensation current measured in the current sampling period, V dc is the voltage of the DC bus, L is the inductance in the main power circuit, C1 and C2 are the two capacitors in the main power circuit, V C1 and V C2 They are the voltages of the two capacitors in the main power circuit, R1 and R2 are the two resistors in the main power circuit, S n is the switching function of the two power half-bridges in the main power circuit;

[0041] The switching function S n Expressed as:

[0042]

[0043] Among them, T n1 is the upper switching device in the power half-bridge, T n2 is the lower switch device in the power half-bridge, n is 1 or 2, representing one of the two half-bridges; the output voltage of the power half-bridge is V SWn Indicates that V SWn =V Cn S n ;

[0044] The cost function g is:

[0045] g=|i Ct (k+1)-i L (k+1)|+d|V C1 (k+1)-V C2 (k+1)|

[0046] Among them, d is the weight coefficient, i Ct is the transient current, i L is the compensation current.

[0047] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0048] (1) The present invention proposes a device for suppressing transient voltage fluctuations on a DC bus, which combines a capacitor with a discharge resistor and allows the capacitor voltage on the device to vary over a wide range. Compared with directly increasing the capacitance, the present invention has a small size, good suppression effect, is insensitive to the size and waveform of the transient current, and has strong robustness.

[0049] (2) The switching signal of the transient voltage fluctuation suppression device of the DC bus of the present invention is obtained through a prediction model, and the optimal switching signal is determined according to the cost function. Compared with the general closed-loop control, it has better dynamic performance and is more suitable for transient working conditions with short duration, making the device more practical. The prediction model can also provide a theoretical basis for further research on the transient voltage fluctuation suppression device.

[0050] (3) The present invention provides a design method for key electrical parameters, which significantly reduces the total capacitance required for the device and the power supply DC bus, avoids the serious consequences caused by DC bus short circuit or bridge arm direct fault, and increases the overall reliability of the power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1A circuit diagram of a device for suppressing transient voltage fluctuations of a DC bus provided by an embodiment of the present invention;

[0052] Figure 2 A flow chart of generating a switch signal by a model predictive control algorithm provided by an embodiment of the present invention;

[0053] Figure 3 The circuit simulation results of the working process of the transient voltage fluctuation suppression device of the DC bus provided by the embodiment of the present invention when the accelerating electrode power supply is turned off. DETAILED DESCRIPTION

[0054] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0055] Example

[0056] like Figure 1 As shown, a device for suppressing transient voltage fluctuations of a DC busbar of an accelerating electrode power supply is connected in parallel to the DC busbar 2 to compensate for transient currents of the DC busbar 2;

[0057] The transient voltage fluctuation suppression device includes: a main power circuit 11, a measuring circuit (not shown), a control circuit (not shown) and a driving circuit (not shown);

[0058] The measuring circuit is used to determine the generation time of the transient current of the DC bus 2 and measure the transient current of the DC bus 2 and the compensation current generated by the main power circuit at the current moment;

[0059] The control circuit obtains a switching signal according to the transient current and the compensation current;

[0060] The driving circuit is connected to the main power circuit 11 and sends the switching signal to the main power circuit 11;

[0061] The main power circuit 11 includes a power switch device (T 11 、T 12 、T 21 and T 22 ) and capacitors (C1 and C2) and a discharge branch 112 composed of mechanical switches (M1 and M2) and resistors (R1 and R2). The discharge branch 112 is connected in parallel to both ends of the capacitor (C1 or C2). The main power circuit 11 controls the power switch device (T 11 、T 12 、T21 and T 22 ) and the state of the mechanical switches (M1 and M2); the transfer branch 111 of the main power circuit controls the power switch device (T 11 、T 12 、T 21 and T 22 ) in an operating state so that the capacitors (C1 and C2) absorb the transient current and generate a compensation current at the next moment to compensate for the transient voltage fluctuation caused by the transient current of the DC bus 2; the discharge branch 112 of the main power circuit controls the mechanical switches (M1 and M2) to close according to the switching signal, and releases the energy absorbed by the capacitors (C1 and C2) through the resistors (R1 and R2), so that the voltage of the capacitors (C1 and C2) returns to the level before the transient current compensation.

[0062] In the transient voltage fluctuation suppression device, the control circuit is connected to the measurement circuit, the drive circuit and the main power circuit. The measurement circuit is connected to the DC bus, and the drive circuit is connected to the main power circuit. The measurement circuit measures the current of the DC bus, determines the time when the DC bus transient current is generated, and measures the transient current and compensation current at the current time and sends them to the control circuit. The control circuit generates a switching signal based on the received transient current and compensation current, and sends the switching signal to the main power circuit through the drive circuit to perform corresponding control on the main power circuit.

[0063] Optional, such as Figure 1 As shown, the main power circuit includes two transfer branches 111, two discharge branches 112 and an inductor. Each transfer branch 111 includes a power half-bridge and a capacitor, and each discharge branch 112 includes a mechanical switch and a resistor.

[0064] A first mechanical switch M1 and a first resistor R1 are connected in series and then connected in parallel across a first capacitor C1. The two ends of the first capacitor C1 are respectively connected to an upper end a and a lower end b of a first power half-bridge. A midpoint e of the first power half-bridge is connected to a first end of an inductor L. The second end of the inductor L is connected to the positive electrode of a DC bus 2. The lower end b of the first power half-bridge is connected to a midpoint f of a second power half-bridge.

[0065] The second mechanical switch M2 is connected in series with the second resistor R2 and then connected in parallel across the second capacitor C2. The two ends of the second capacitor C2 are respectively connected to the upper end g and the lower end h of the second power half bridge. The lower end h of the second power half bridge is connected to the negative electrode of the DC bus 2.

[0066] Each power half-bridge is composed of two power switching devices, and the power switching devices in each power half-bridge are turned on or off in a complementary manner.

[0067] Figure 1 In, V dcis the DC bus voltage of the accelerating pole power supply (AGPS), which is 2500V. dc is the DC bus capacitance of the accelerating electrode power supply, i Ct It is the transient current when AGPS turns off the rectifier and inverter. The transient voltage fluctuation suppression device is connected in parallel with the DC bus to compensate for the transient current of the DC bus. The transient voltage fluctuation suppression device includes: main power circuit, measurement circuit, control circuit and drive circuit. Figure 1 As shown, the main power circuit includes a transfer branch consisting of power switching devices and capacitors and a discharge branch consisting of mechanical switches and resistors. 11 、T 12 、T 21 、T 22 It is composed of four insulated gate bipolar transistors (IGBTs), which are connected in pairs to form two half-bridges. After the outputs of the two half-bridges are connected in series, one end is connected to the ground potential of the AGPS DC bus, and the other end is connected to the high potential of the DC bus through the inductor L.

[0068] When AGPS is working normally, the controller does not generate a switch control signal. Figure 1 The four IGBTs are turned off, T 12 and T 21 It is completely shut down, only T 12 and T 22 The anti-parallel diode in the middle is turned on, and C1 and C2 are charged from the DC bus.

[0069] When AGPS is turned off, the DC bus generates transient current. Since the inverter shutdown time is much shorter than the rectifier, the transient current i Ct Mainly composed of the rectifier current i rt constitute, so i Ct Approximately equal to i rt The measurement circuit detects the moment when the transient current of the DC bus is generated, that is, the moment when the AGPS is turned off, and at this moment the output current i rt Sampling. The capacitors C1 and C2 in the transfer branch absorb the transient current of the DC bus. The transfer branch generates a compensation current on the inductor L by controlling the power switch device. The measurement circuit measures the transient current of the DC bus and the compensation current generated by the main power circuit on the inductor L. The control circuit adjusts the sampling period T according to the transient current and the compensation current. s The switching signal is generated in the main power circuit, and the compensation current of the next moment is generated according to the switching signal. By adjusting the switching signal, the compensation current is equal to the transient current in magnitude and opposite in direction, thereby reducing the transient current of the DC bus capacitor and reducing the transient voltage fluctuation of the DC bus. CtWhen it drops to 0, the device stops generating the switching signal. At this time, the capacitor voltage V Cn When the peak value is reached, the mechanical switches M1 and M2 in the discharge branch are turned on, and R1 and R2 act as discharge resistors, releasing the energy absorbed by capacitors C1 and C2 through the resistors, making V Cn The device then waits for the next AGPS shutdown command. The above is a complete working cycle of the device.

[0070] Furthermore, since the two half-bridge structures and parameters are exactly the same, the capacitor voltage V of C1 and C2 when charging reaches steady state is C1 and V C2 are equal and equal to V dc / 2.

[0071] In the transient working process after AGPS is turned off, the switching signal model predictive control algorithm of the transient voltage fluctuation suppression device is determined. Figure 1 The prediction model of the main power loop circuit of the transient voltage fluctuation suppression device is derived.

[0072] Optionally, the transfer branch is connected in series with two power half-bridge outputs, each power half-bridge is composed of two switching devices, and the switching devices in each power half-bridge are complementary turned on or off;

[0073] When the upper switch device is turned on and the lower switch device is turned off, the switching signal of the power half-bridge can be expressed by the switching function S n =1 indicates that when the upper switch device is turned off and the lower switch device is turned on, the switching signal of the power half-bridge can be expressed by the switching function S n =0 represents; wherein n is 1 or 2, representing one of the two half bridges.

[0074] The switching state of the power half-bridge can be expressed by the switching function S n Indicates that:

[0075]

[0076] The output voltage of the power half-bridge is V SWn Indicates that V SWn =V Cn S n .

[0077] Optionally, the control circuit uses a model predictive control algorithm to determine the switching signal according to the transient current and the compensation current;

[0078] When the measurement circuit detects that the DC bus generates transient current, the control circuit performs the sampling cycle T s Generate a switch signal in

[0079] If the current of the inductor L is measured to be i L (k), then the compensation current i of the transient voltage fluctuation suppression device in the next sampling period is determined according to the model predictive control algorithm. L (k+1) is:

[0080]

[0081] Capacitor voltage V Cn (k+1) is:

[0082]

[0083] Among them, i L (k) is the compensation current measured in the current sampling period, V dc is the voltage of the DC bus, L is the inductance in the main power circuit, C1 and C2 are the two capacitors in the main power circuit, V C1 and V C2 They are the voltages of the two capacitors in the main power circuit, R1 and R2 are the two resistors in the main power circuit, S n It is the switching function of the two power half-bridges in the main power circuit.

[0084] According to the volt-ampere characteristics of capacitance and resistance, when the mechanical switch is turned on, C n and R n The sum of the branch currents can be expressed as:

[0085]

[0086]

[0087] Among them, i L is the inductor current of the device.

[0088] In the control system, all variables are discrete. The controller samples the measurement signal periodically and performs the calculation process within the timer time. The sampling period is T. s The capacitor voltage in the current sampling period can be expressed as V Cn (k), the capacitor voltage in the next sampling period is expressed as V Cn (k+1). Therefore, the above formula is discretized and expressed as:

[0089]

[0090]

[0091] The capacitor voltage in the next sampling period is obtained as:

[0092]

[0093] The inductor current in the next sampling period is:

[0094]

[0095] The sampling frequency of the controller can reach tens of kHz, so T s <<1s, T in the above formula s 2 The term can be ignored and the above formula can be simplified to:

[0096]

[0097] Under the condition that the current capacitor voltage and inductor current are known, different switching functions will generate different capacitor voltages and inductor currents at the next moment. The above is the prediction model of the transient voltage fluctuation suppression device.

[0098] The inductor current i of the transient voltage fluctuation suppression device L During shutdown, the dc The transient current i Ct The transient current of the capacitor in the transient voltage fluctuation suppression device is greatly reduced, thereby reducing the transient voltage fluctuation of the DC bus. Ct is the reference current of the device, i L Need to i Ct Fast and accurate tracking. Because in each sampling period, the different conduction states of the power switching devices in the two half-bridges correspond to different switching functions S n , generate different switching signals, can generate different i L Waveforms, in order to achieve the desired control effect, these different switching states need to be evaluated.

[0099] Optionally, the compensation current i corresponding to different switching signals is calculated by the cost function L The switch signal corresponding to the minimum cost function is selected as the target switch signal, and the main power circuit is controlled according to the target switch signal to generate the compensation current i L With transient current i Ct Equal in size and opposite in direction;

[0100] The cost function g is:

[0101] g=|i Ct (k+1)-i L (k+1)|+d|V C1 (k+1)-V C2 (k+1)|

[0102] Among them, d is the weight coefficient, i Ct is the transient current, i L To compensate the current; in one sampling cycle, traverse all possible combinations of the switching function (S1 and S2) and predict the i of the next sampling cycle L (k+1) and V Cn (k+1), and calculate the corresponding cost function g.

[0103] Since the two half-bridges of this device are completely symmetrical, the voltage difference between the two capacitors (C1 and C2) is very small, so d can be smaller. In this example, d is set to 0.5.

[0104] In each sampling period, S1 and S2 have two possibilities: 0 or 1. Therefore, there are four combinations of switch states x (i.e., x = 0, 1, 2, 3), which will make the cost function have four different values. Selecting the switch state corresponding to the minimum value indicates that this set of switch signals can make i L with i Ct The difference is the smallest, which best meets our needs. This set of switch states is the switch state required in the current sampling period. The controller generates the corresponding switch control signal to make the current of the device close to i Ct Compared with the general proportional-integral-derivative (PID) closed-loop control method that generates pulse width modulation (PWM) switching signals, model predictive control has better dynamic performance and is more suitable for suppressing transient voltage fluctuations in the DC bus capacitor of AGPS.

[0105] Furthermore, the flow chart of determining the switch signal according to the model predictive control algorithm is as follows: Figure 2 When the AGPS shutdown command is detected, the device starts working. First, the mechanical switch is turned on, and the device absorbs transient current and discharges at the same time. Since charging is much faster than discharging, the time constant is not in the same order of magnitude, so the discharge process during charging can be ignored. Then the capacitor voltage V of the device at the current moment is measured. Cn (k) and the inductor current i L (k), x is 1 to 4 to represent the number of different switch signal combinations, and the inductor current i at the next moment is calculated according to the prediction model. Lx (k+1) and capacitor voltage V Cnx (k+1), and then calculate the cost function g x , by comparing g x The size of traversal to obtain g x The optimal value (i.e. minimum value) of , and then generate a switching signal. Until the transient current i rt When it drops to 0, the device stops generating the switching signal. Cn reaches a peak value, and then discharges through the mechanical switch and the resistance branch, making V CnDecrease until it reaches the steady-state value (0.5V) charged before operation dc , i.e. 1250V), the mechanical switch is turned off, and then waits for the next shutdown command from AGPS.

[0106] By adopting a fast-response predictive model control algorithm to generate appropriate switching signals, the transient current of the DC bus can be tracked and compensated quickly and accurately on the transient voltage fluctuation suppression device.

[0107] The design calculations for other electrical parameters of the transient voltage fluctuation suppression device are as follows.

[0108] Optionally, the capacitor C n The value range of is:

[0109]

[0110] Among them, V Cm is the maximum value allowed for the capacitor voltage, E off It is the energy during the duration of the transient current, and the calculation formula is:

[0111]

[0112] Resistor R n The value range of is:

[0113]

[0114] Among them, t rs is the period of transient current that the transient voltage fluctuation suppression device needs to compensate, t off is the duration of the transient current to be compensated.

[0115] Resistor R n The power P that needs to be met Rn for:

[0116]

[0117] During the shutdown period, each capacitor in the discharge branch of the transient voltage fluctuation suppression device absorbs the energy E of the transient current of the AGPS DC bus capacitor. off ,for:

[0118]

[0119] The absorbed energy will cause the capacitor voltage of the device to increase. Excessive capacitor voltage will cause the capacitor itself and the switching device of the device to break down, so it needs to be controlled within a certain range. Cm V before the device is activated C1 or V C2The preset multiple is greater than 1. Considering the voltage resistance and usage of the capacitor, the peak value V Cm It is 1.6 times the voltage before operation, that is, 1.6×1250=2000V. According to the law of capacitor energy storage, the capacitance value range of the device can be obtained as follows:

[0120]

[0121] This energy will eventually be released to the resistor R n Assume that the AGPS off period is t rs , then the power of the resistor is:

[0122]

[0123] In addition, the resistance of the resistor must be small enough so that V Cn The next time AGPS is turned off, it can drop from the peak value to the steady-state voltage during charging. According to the voltage drop law of the RC discharge circuit, the resistance range of the resistor is:

[0124]

[0125] The mechanical switches in the device need to withstand 0.5V dc capacitor voltage, and 0.5V dc / R n Since mechanical switches are well developed, such mechanical switch parameter requirements are easy to meet.

[0126] The inductance of the device will affect the i L The change rate of the inductance is very important, so the selection of the inductance value is also very important. This example uses the model predictive control method to pursue fast dynamic response capability, but the switching frequency of this control method is not fixed. When the inductance value is small, i L Will soon depart from rt , in order to make i L Successfully tracked i rt And controlled within a certain error range, the switching state of the device needs to be switched frequently. Therefore, under the premise of constant sampling frequency, the smaller the inductance, the higher the actual switching frequency f sw The higher the sampling frequency T s is f sw The upper limit of , because according to the control principle, only one switching signal is generated in one sampling period.

[0127] In summary, the sampling frequency and inductance value will affect the switching frequency of the device. The difference in switching frequency will result in i L The fluctuation range △i L Different. The higher the actual switching frequency, the L Trackingrt The smaller the error, the higher the loss of the switching device. The switching frequency is determined by factors such as device type, power capacity, and heat dissipation conditions. In this example, the inductance of the device is selected as 250μH, the sampling frequency is selected as 25kHz, and i L The ripple rate i Lr % is within 20%.

[0128] According to the above design process and control method, the circuit simulation results of the device in transient current compensation of AGPS are shown in Figure 3 , where C n 5mF, R n is 40Ω, the transient current i Ct It lasts for 4.89ms. It can be seen that during the period when the transient current drops to 0, the inductor current i L Able to quickly and accurately track DC bus transient current, i L The ripple rate i Lr The actual switching frequency is 27 / 4.89 = 5.52kHz, and the peak value of the capacitor voltage is 1899.9V, which is less than the allowed peak value (2000V). This shows that the above design process and model predictive control are correct and reasonable.

[0129] The technical solution of the present invention connects two power half-bridge outputs in series and connects them to the DC bus via an inductor. A discharge circuit consisting of a mechanical switch and resistor is added to suppress transient DC voltage fluctuations. The model predictive control method applied to the DC bus transient voltage fluctuation suppression device generates appropriate switching signals, achieving improved dynamic performance. During DC bus transients, it rapidly tracks and compensates for transient currents in the DC bus, reducing transient voltage fluctuations in the accelerating electrode power supply. Due to its millisecond-level dynamic response capability, it can reduce the amount of DC bus capacitors used.

[0130] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A device for suppressing transient voltage fluctuations of a DC bus, characterized in that: The transient voltage fluctuation suppression device is connected in parallel to both ends of the DC bus, and the transient voltage fluctuation suppression device includes: a main power circuit, a measurement circuit, a control circuit and a drive circuit; The measuring circuit is used to determine the generation time of the DC bus transient current and measure the transient current at the current time and the compensation current generated by the main power circuit; The control circuit obtains a switching signal according to the transient current and the compensation current; The driving circuit is connected to the main power circuit and sends the switching signal to the main power circuit; The main power circuit includes two transfer branches, two discharge branches and one inductor, each of the transfer branches includes one power half-bridge and one capacitor, and each of the discharge branches includes one mechanical switch and one resistor; A first mechanical switch and a first resistor are connected in series and then connected in parallel across a first capacitor. The two ends of the first capacitor are respectively connected to an upper end and a lower end of a first power half-bridge. The midpoint of the first power half-bridge is connected to a first end of the inductor. The second end of the inductor is connected to a positive electrode of a DC bus. The lower end of the first power half-bridge is connected to a midpoint of a second power half-bridge. A second mechanical switch and a second resistor are connected in series and then connected in parallel across a second capacitor, wherein the two ends of the second capacitor are respectively connected to an upper end and a lower end of a second power half-bridge, and the lower end of the second power half-bridge is connected to the negative electrode of the DC bus; Each power half-bridge is composed of two power switching devices, and the power switching devices in each power half-bridge are complementary turned on or off; The transfer branch is used to control the state of the power switching device according to the switching signal, so that the capacitor absorbs the transient current and generates a compensation current at the next moment to compensate for the transient voltage fluctuation caused by the transient current; the discharge branch is used to control the closing of the mechanical switch according to the switching signal to release the energy absorbed by the capacitor through the resistor.

2. The transient voltage fluctuation suppression device according to claim 1, characterized in that: The power switch device includes a diode; When the DC bus operates normally, the power switching devices and the mechanical switches are all turned off, and the capacitor of each power half-bridge is charged from the DC bus through the diode.

3. The transient voltage fluctuation suppression device according to claim 1, characterized in that: The capacitor C n The value range of is: Among them, V Cm is the maximum value allowed for the capacitor voltage, n is 1 or 2, E off It is the energy during the duration of the transient current, and the calculation formula is: The resistor R n The value range of is: Among them, t rs is the period of transient current that the transient voltage fluctuation suppression device needs to compensate, t off is the duration of the transient current to be compensated, and n is 1 or 2; The resistor R n The power P that needs to be met Rn for:

4. A method for suppressing transient voltage fluctuations of a DC bus, applied to the device for suppressing transient voltage fluctuations of a DC bus according to any one of claims 1 to 3, characterized in that: include: The measuring circuit determines the generation time of the DC bus transient current and measures the transient current at the current moment and the compensation current generated by the main power circuit; The control circuit obtains the transient current and the compensation current, and determines a switching signal according to a model predictive control algorithm; The driving circuit sends the switching signal to the main power circuit; The main power circuit includes two transfer branches, two discharge branches and one inductor, each of the transfer branches includes one power half-bridge and one capacitor, and each of the discharge branches includes one mechanical switch and one resistor; A first mechanical switch and a first resistor are connected in series and then connected in parallel across a first capacitor. The two ends of the first capacitor are respectively connected to an upper end and a lower end of a first power half-bridge. The midpoint of the first power half-bridge is connected to a first end of the inductor. The second end of the inductor is connected to a positive electrode of a DC bus. The lower end of the first power half-bridge is connected to a midpoint of a second power half-bridge. A second mechanical switch and a second resistor are connected in series and then connected in parallel across a second capacitor, wherein the two ends of the second capacitor are respectively connected to an upper end and a lower end of a second power half-bridge, and the lower end of the second power half-bridge is connected to the negative electrode of the DC bus; Each power half-bridge is composed of two power switching devices, and the power switching devices in each power half-bridge are complementary turned on or off; The main power circuit controls the state of the power switching device of the transfer branch according to the switching signal, so that the capacitor absorbs the transient current and generates a compensation current at the next moment to compensate for the transient voltage fluctuation caused by the transient current; the main power circuit controls the closing of the mechanical switch of the discharge branch according to the switching signal, and releases the energy absorbed by the capacitor of the transfer branch through the resistor.

5. The method according to claim 4, characterized in that The measuring circuit measures the current of the rectifier of the DC bus at the current moment and determines it as the transient current; The measurement circuit measures the current generated by the transfer branch on the inductor L at the current moment and determines it as the compensation current.

6. The method according to claim 5, characterized in that The control circuit obtains the transient current and the compensation current, and determines a switching signal through a model predictive control algorithm, including: When the measurement circuit detects that the DC bus generates transient current, the control circuit traverses all possible combinations of the switching function in one sampling cycle and predicts the i of the next sampling cycle. L (k+1) and V Cn (k+1); Calculate the cost function of each predicted compensation current and select the switching signal corresponding to the minimum cost function value as the target switching signal; If the current generated by the transfer branch on the inductor L at the current moment is measured to be i L (k), then the compensation current i at the next moment is determined according to the model predictive control algorithm L (k+1) is: Capacitor voltage V Cn (k+1) is: Among them, i L (k) is the compensation current measured in the current sampling period, V dc is the voltage of the DC bus, L is the inductance in the main power circuit, C1 and C2 are the two capacitors in the main power circuit, V C1 and V C2 They are the voltages of the two capacitors in the main power circuit, R1 and R2 are the two resistors in the main power circuit, S n is the switching function of the two power half-bridges in the main power circuit; The switching function S n Expressed as: Among them, T n1 is the upper switching device in the power half-bridge, T n2 is the lower switch device in the power half-bridge, n is 1 or 2, representing one of the two half-bridges; the output voltage of the power half-bridge is V SWn Indicates that V SWn =V Cn S n ; The cost function g is: g=|i Ct (k+1)-i L (k+1)|+d|V C1 (k+1)-V C2 (k+1)| Among them, d is the weight coefficient, i Ct is the transient current, i L is the compensation current.

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