A voltage equalization system and control method applied to a non-controlled rectifier valve

Abstract

A kind of voltage equalization system and control method applied to uncontrolled rectifier valve, uncontrolled rectifier valve includes multiple series diodes, voltage equalization system includes multiple voltage equalization units, voltage equalization unit is used to adjust the voltage balance of series diode, voltage equalization unit includes voltage stabilizing module, first resistance, energy storage module, switch module, second resistance and control module;Control method includes: the voltage signal of each series diode is collected, and compared with the mean voltage of set series diode, the voltage difference is calculated;Voltage difference is through PI integral operation, and the equivalent impedance of series diode is measured in real time;Equivalent impedance is adjusted to set mean impedance, and then the voltage value of voltage signal is adjusted;The voltage signal after adjustment is carried out negative feedback, and voltage difference is continuously reduced;The voltage balance of series diode in the uncontrolled rectifier valve can be realized in the present application, and the purpose of simple and easy parameter design, small loss and uncontrolled rectifier valve independent modulation operation.

Description

Technical Field

[0001] This invention relates to the field of uncontrolled rectifier valves, and more specifically to a pressure equalization system and control method for uncontrolled rectifier valves. Background Technology

[0002] Uncontrolled rectifier valves are an important rectifier component in the high-voltage direct current (HVDC) transmission network structure. They are lightweight, have a small footprint, and are easy to maintain. They have also seen rapid development and application in lightweight HVDC transmission systems based on medium-frequency (400Hz) rectification.

[0003] Series diodes are the core component of uncontrolled rectifier valves, characterized by large conduction current, high withstand voltage, and low cost. However, the differences in parameters such as diode junction capacitance, internal resistance, and reverse recovery time result in uneven voltage distribution during the turn-off and blocking states of the series diodes, causing some diodes to break down and endangering the safe and stable operation of the uncontrolled rectifier valve. Therefore, maintaining voltage balance when the series diodes are off is a challenge in the field of uncontrolled rectifier valves.

[0004] Currently, the method proposed in technical document 1, "Voltage Distribution and Voltage Equalization Problem of Series Diode Rectification", which involves connecting a voltage equalization resistor in parallel to a multi-stage series diode, can suppress diode current overshoot and thus achieve voltage equalization of multi-stage diodes in series. However, the buffer loss generated by this method is relatively large in high-voltage applications.

[0005] Technical document 2, "Optimization Design of RC Snubber Circuit", provides a method for achieving voltage equalization of series diodes by connecting parallel RC snubber circuits. The RC snubber circuit can effectively absorb the voltage spike when the diode is turned off to achieve the effect of voltage equalization. However, in high-voltage applications, the RC snubber circuit has large losses and large size.

[0006] Technical document 3, "Research on SiC MOSFET Driving and Buffering Technology," provides an RCD buffer circuit suitable for high-voltage direct current transmission. This circuit can suppress excessive current change rate and excessive voltage spikes, ensuring balanced voltage distribution across the series diodes. However, the RCD buffer circuit still suffers from the complexity of RC parameter tuning: First, the minimum resistance value must meet the diode's current limit, and the maximum value must meet the diode's RC discharge cycle. Second, the capacitance value determines the absorption effect of voltage spikes; a larger capacitance results in smaller voltage spikes and lower diode turn-off losses, leading to better voltage equalization. However, this increases the circuit size, and the maximum capacitance value must also meet the diode's RC discharge cycle.

[0007] Meanwhile, existing technology requires manual adjustment of the parameters of each device according to different overvoltage conditions of series diodes, and the uncontrolled rectifier valve cannot be independently modulated and operated;

[0008] Therefore, in the existing technology of uncontrolled rectifier valves, there are problems such as complex parameter design, large losses, and the inability of uncontrolled rectifier valves to operate independently. Summary of the Invention

[0009] To overcome the shortcomings of the prior art, the present invention provides a voltage equalization system and control method for uncontrolled rectifier valves. The purpose is to solve the technical problems of complex parameter settings, large losses, and the inability of uncontrolled rectifier valves to operate independently in series diode voltage equalization technology, and to achieve the goals of simple parameter design, low losses, and independent operation of uncontrolled rectifier valves.

[0010] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0011] A voltage equalization system for an uncontrolled rectifier valve includes multiple series diodes connected in series in the arms of a three-phase voltage circuit. The voltage equalization system includes multiple voltage equalization units, each used to regulate the voltage balance of the series diodes. Each voltage equalization unit includes a voltage regulator module, a first resistor, an energy storage module, a switching module, a second resistor, and a control module. The first terminal of the voltage regulator module is connected to the negative terminal of the series diodes. The second terminal of the voltage regulator module is connected to the first terminal of the first resistor and the first terminal of the energy storage module. The second terminal of the energy storage module is connected to the first terminal of the switching module and the first terminal of the second resistor. The positive terminal of the series diodes is connected to the second terminal of the first resistor, the second terminal of the switching module, and the second terminal of the second resistor. The control terminal of the switching module is connected to the control module, which is used to control the switching on and off of the switching module.

[0012] A current-conducting diode is also provided between the energy storage module and the second resistor. The positive terminal of the current-conducting diode is connected to the second terminal of the energy storage module, and the negative terminal of the current-conducting diode is connected to the first terminal of the second resistor.

[0013] The voltage regulator module includes a first capacitor, which is used to filter out overvoltage signals from the series diode.

[0014] The energy storage module includes a first inductor, which stores overvoltage signals and conducts current through a first resistor and a second resistor.

[0015] A pressure equalization control method applied to an uncontrolled rectifier valve, wherein the pressure equalization system described above includes:

[0016] The voltage signals of each series diode are collected and compared with the set average voltage of the series diodes to calculate the voltage difference; the voltage difference is integrated by PI and the equivalent impedance of the series diodes is measured in real time; the equivalent impedance is adjusted to the set average impedance, thereby adjusting the voltage value of the voltage signal; the adjusted voltage signal is negatively fed back to continuously reduce the voltage difference.

[0017] Calculate the total impedance of each series diode and the arm voltage of the three-phase voltage circuit. The ratio of the voltage signal value to the arm voltage value is equal to the ratio of the equivalent impedance to the total impedance.

[0018] The control module adjusts the equivalent impedance by controlling the duty cycle of the switching module.

[0019] The control module uses DC chopper to adjust the duty cycle of the switching module.

[0020] The average voltage is the average of the steady-state voltages of each series-connected diode when it is turned off.

[0021] Compared with existing technologies, the advantages of this invention are as follows: The voltage regulator module filters out overvoltage signals, reducing the voltage change rate of the series diodes; the energy storage module stores energy in the overvoltage signal and conducts current through the first and second resistors, achieving dynamic buffering of the diodes; the switching module adjusts the equivalent resistance of the series diodes by turning them on and off, suppressing the current change rate and reducing losses; its parameter design only includes the duty cycle parameter of the switching module, simplifying parameter design; a control method is introduced into the voltage equalization system to perform negative feedback adjustment and PI integral calculation of the voltage difference of the series diodes, reducing the voltage difference between the voltage signal and the average voltage; the voltage signal of the series diodes dynamically tracks the average voltage of the bridge arm in real time, optimizing the voltage equalization effect of the series diodes and achieving independent modulation operation without controlling the rectifier valve.

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the circuit structure of the uncontrolled rectifier valve according to an embodiment of the present invention;

[0025] Figure 2 This is a simplified schematic diagram of a series diode according to an embodiment of the present invention;

[0026] Figure 3 The equivalent circuit diagram of the bridge arm cutoff voltage of the series diode in an embodiment of the present invention is shown.

[0027] Figure 4 This is a schematic diagram of the voltage equalization unit circuit according to an embodiment of the present invention;

[0028] Figure 5 This is a schematic diagram of the feedback structure of the pressure equalization control method according to an embodiment of the present invention;

[0029] Figure 6 This is a parameter diagram of the uncontrolled rectifier valve according to an embodiment of the present invention;

[0030] Figure 7 This is a simulation structure parameter diagram of an embodiment of the present invention;

[0031] Figure 8 A voltage parameter diagram of the series diode in an embodiment of the present invention with respect to voltage equalization system;

[0032] Figure 9 This is a voltage parameter diagram of the series diode in a conventional voltage equalization system according to an embodiment of the present invention;

[0033] Figure 10 The diagram shows the voltage parameters of the series diodes in the voltage equalization system according to an embodiment of the present invention. Detailed Implementation

[0034] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0035] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0036] A pressure equalization system applied to an uncontrolled rectifier valve, such as Figure 1 As shown, the uncontrolled rectifier valve includes an AC power supply AC, a transformer T, a line inductance LE, and multiple series diodes. The voltage equalization system includes multiple voltage equalization units 1, which are used to adjust the voltage balance of the series diodes when they are turned off.

[0037] The output terminal of the AC power supply is connected to the input terminal of the transformer T. The output terminal of the transformer T is connected to the three-phase voltage circuit. Each phase of the three-phase voltage circuit is connected to the line inductor LE. The first end of the line inductor LE is connected to the three-phase voltage circuit, and the second end of the line inductor LE is connected to a series diode. Multiple series diodes in each phase circuit are connected in series sequentially, including the first series diode, the second series diode, ..., the nth series diode, and corresponding to the first voltage equalization unit 1, the second voltage equalization unit 1, ..., the nth voltage equalization unit 1.

[0038] The parameters of a series diode are related to its operating voltage. A series diode is a typical semiconductor device. In the space charge region, the amount of charge changes with the applied voltage and exhibits a capacitance effect, which is called junction capacitance. According to different mechanisms, junction capacitance can be divided into diffusion capacitance and barrier capacitance. The capacitance value of barrier capacitance and diffusion capacitance are related to the applied reverse voltage and the applied forward voltage, respectively. Therefore, the junction capacitance effect of a series diode needs to be considered when it is in operation.

[0039] The series diode can be further simplified during the transient process as follows: Figure 2 As shown; where Vd is the voltage across the series diode; when the series diode is forward-biased, it can be equivalent to a parallel model of diffusion capacitor CF and diffusion resistor RF; when the series diode is reverse-biased, it can be equivalent to a barrier capacitor CR; when the series diode string is forward-biased, the voltage drop of each diode is zero, and there is no voltage distribution or withstand voltage problem; when the series diode string is reverse-biased, each series diode needs to withstand an extremely high DC voltage, and an additional voltage equalization unit 1 is required to achieve dynamic steady-state balance of the reverse voltage of the series diode.

[0040] At cutoff, the voltage equivalent circuit of the bridge arm is as follows: Figure 3 As shown, taking the m-th series diode as an example, the voltage amplitude of the m-th series diode is calculated by formula (1):

[0041] (1)

[0042] in, Let be the voltage during the cutoff process of the m-th series diode. For bridge arm voltage, Let be the barrier capacitance of the m-th series-connected diode. For the inductance of the series bridge arm, The line angular frequency, The impedance is the barrier capacitance of the series diode. For inductive impedance, This is the total impedance of the barrier capacitance of the series diodes on the bridge arm.

[0043] Dynamic steady-state equilibrium of the reverse voltage of the series diodes is achieved by using voltage equalization unit 1.

[0044] like Figure 4 As shown, the voltage equalization unit 1 includes a voltage regulator module 10, a first resistor R1, an energy storage module 11, a switch module 12, a second resistor R2, and a control module 13. The voltage regulator module 10 is used to stabilize the voltage signal of the series diode when it is turned off. The energy storage module 11 is used to store the overvoltage signal generated by the series diode when it is turned off, and conducts it through the first resistor R1 and the second resistor R2. The control module 13 is used to control the switching module 12 to turn on and off, thereby realizing the connection and disconnection of the second resistor R2 and the energy storage module 11.

[0045] The first terminal of the voltage regulator module 10 is connected to the negative terminal of the series diode. The second terminal of the voltage regulator module 10 is connected to the first terminal of the first resistor R1 and the first terminal of the energy storage module 11. The second terminal of the energy storage module 11 is connected to the first terminal of the switch module 12 and the first terminal of the second resistor R2. The positive terminal of the series diode is connected to the second terminal of the first resistor R1, the second terminal of the switch module 12 and the second terminal of the second resistor R2. The control terminal of the switch module 12 is connected to the control module 13.

[0046] A current-conducting diode M2 ​​is also provided between the energy storage module 11 and the second resistor R2. The current-conducting diode M2 ​​is used to enable the rapid flow of current between the energy storage module 11 and the second resistor R2. The positive terminal of the current-conducting diode M2 ​​is connected to the second terminal of the energy storage module 11, and the negative terminal of the current-conducting diode M2 ​​is connected to the first terminal of the second resistor R2.

[0047] The voltage regulator module 10 includes a first capacitor C1, the capacitance value of which is set according to the voltage value of the series diode when it is turned off; the energy storage module 11 includes a first inductor L1, the inductance value of which is set according to the overvoltage signal of the series diode; the switching module 12 includes a first switching transistor M1, which is a high-frequency switching transistor; and the current-conducting diode M2 ​​is a fast recovery diode.

[0048] By controlling the on and off states of the first switching transistor M1, the second resistor R2 can be switched on and off when the cutoff voltage of the series diode is large, thereby adjusting the equivalent impedance of the series diode and thus adjusting the cutoff voltage of the series diode.

[0049] The voltage difference is calculated by subtracting the voltage signal of the series diode from the average voltage. The input of the PI controller receives the voltage difference, and the output of the PI controller is connected to the input of the control module 13. The output of the control module 13 is connected to the control terminal of the switch module 12. The PI controller is used to perform integral calculation on the voltage difference and output the integral signal to the control module 13. The control module 13 is used to receive and control the switching module 12 to turn on and off according to the integral signal.

[0050] A pressure equalization control method for an uncontrolled rectifier valve, the method employing the aforementioned pressure equalization system for an uncontrolled rectifier valve, the method comprising:

[0051] Set the average voltage and corresponding average impedance of the series diodes when they are turned off; collect the voltage signals of each series diode and compare them with the average voltage to calculate the voltage difference; perform PI integration on the voltage difference and measure the equivalent impedance of the series diodes in real time; adjust the equivalent impedance to the average impedance, thereby adjusting the voltage value of the voltage signal; apply negative feedback to the adjusted voltage signal and continuously reduce the voltage difference.

[0052] The calculation involves the total impedance of each series diode and the arm voltage of the three-phase voltage circuit. The average voltage is the average value of the steady-state voltage of each series diode when it is turned off. The average voltage is obtained by dividing the arm voltage value equally among the series diodes. The ratio of the voltage signal value to the arm voltage value is equal to the ratio of the equivalent impedance to the total impedance.

[0053] like Figure 5 As shown, specifically, the non-inverting input of the PI controller receives the voltage signal from the series diode, and the inverting input of the PI controller receives the set average voltage. The voltage signal is compared with the average voltage to obtain the voltage difference, and the PI controller performs integration on the voltage difference.

[0054] The PI controller outputs the result of the integral calculation to the control module 13, and the control module 13 adjusts the equivalent impedance of the series diode according to the set average impedance.

[0055] Specifically, the control module 13 adjusts the equivalent impedance by controlling the duty cycle of the switch module 12.

[0056] Furthermore, the control module 13 uses DC chopping to adjust the duty cycle of the switching module 12.

[0057] Specifically, taking the i-th voltage equalization unit 1 as an example, where 1≤i≤n, when the duty cycle of the current-conducting diode M2 ​​is... When the series diode is connected, the equivalent impedance is calculated using formula (2):

[0058] (2)

[0059] In the i-th equalization unit 1 Let be the equivalent impedance of the i-th series diode. The impedance of the first capacitor C1 is... The resistance of the first resistor R1 is... The resistance of the second resistor R2 is... The impedance of the first inductor L1, This is the duty cycle of the first switching transistor M1.

[0060] Perform a Fourier transform on equation (2) and obtain the equivalent impedance of the series diode in the complex frequency domain, which is calculated as equation (3):

[0061] (3)

[0062] in, Let C1 be the impedance of the first capacitor C1 in the complex frequency domain. Let L1 be the impedance of the first inductor in the complex frequency domain.

[0063] Therefore, the voltage value of the voltage signal of the series diode can be obtained from the duty cycle of the first switching transistor M1 using formula (4):

[0064] (4)

[0065] In the i-th equalization unit 1 The voltage value is the voltage signal of the series diode. The voltage on the bridge arm, This is the equivalent impedance of the series diode. This is the total impedance of the diodes connected in series on the bridge arm.

[0066] The control module 13 adjusts the equivalent impedance of the series diode by controlling the duty cycle of the switch module 12, thereby adjusting the voltage value of the voltage signal of the series diode. The adjusted voltage signal is negatively fed back and compared with the average voltage. The PI controller further integrates the voltage difference. The control module 13 readjusts the duty cycle of the first switch M1 to continuously reduce the voltage difference. Thus, the voltage signal of the series diode can dynamically track the average voltage of the bridge arm in real time, optimizing the voltage equalization effect of the series diode.

[0067] Furthermore, the parameter table for the uncontrolled rectifier valve is as follows: Figure 6 As shown, the simulated structural parameters such as power supply voltage, inductance, and transformer are as follows: Figure 7 As shown, simulation analysis was performed after setting the parameters of the uncontrolled rectifier valve.

[0068] like Figure 8 As shown, in the absence of a voltage equalization system, the voltage distribution of each series diode shows that the steady-state voltages of each diode when it is turned off are 10630V, 11060V, and 10840V, respectively, with a voltage range of 430V. Without a voltage equalization circuit, the voltage range and voltage distribution waveform amplitude of the diodes fluctuate greatly.

[0069] like Figure 9As shown, in the case of a traditional voltage equalization system, the voltage distribution of each series diode is as follows. It can be seen that when the capacitance value in the voltage equalization system changes, that is, when the voltage equalization capacitor ages and causes uneven voltage, the steady-state voltages of each diode when it is turned off are 10880V, 10860V, and 10820V, respectively, with a voltage range of 60V. Therefore, the traditional voltage equalization system reduces the fluctuation of the voltage range to a certain extent, but its diode voltage distribution waveform still has obvious fluctuations and fails to improve the adverse effect of voltage equalization capacitor aging on the voltage equalization effect of series diodes.

[0070] like Figure 10 As shown in the figure, under the condition of this voltage equalization system, the voltage distribution of each series diode shows that when the capacitance value of this voltage equalization system changes, that is, when the capacitor ages, the steady-state voltages of each diode when it is turned off are 10860V, 10870V, and 10860V respectively; the voltage difference is 10V. Therefore, when the capacitor ages, just like in the traditional voltage equalization system, this voltage equalization system can also control the voltage balance of each diode port in real time, so that the voltage difference between each diode is kept at a small level.

[0071] Simulation results show that the diode voltage difference in this voltage equalization system is reduced by 43 times compared to the diode voltage difference in the system without voltage equalization, and by 6 times compared to the diode voltage difference in the traditional voltage equalization system.

[0072] In this invention, an overvoltage signal is filtered out by a voltage regulator module, reducing the voltage change rate of the series diodes; an energy storage module stores energy in the overvoltage signal and conducts current through a first resistor and a second resistor, achieving dynamic buffering of the diodes; the switching module adjusts the equivalent resistance of the series diodes by turning them on and off, suppressing the current change rate and reducing losses; its parameter design only includes the duty cycle parameter of the switching module, making parameter design simple; a control method is introduced into the voltage equalization system to perform negative feedback adjustment and PI integral calculation of the voltage difference of the series diodes, reducing the voltage difference between the voltage signal and the average voltage; the voltage signal of the series diodes dynamically tracks the average voltage of the bridge arm in real time, optimizing the voltage equalization effect of the series diodes and achieving the effect of independent modulation operation without controlling the rectifier valve.

[0073] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A voltage equalization system applied to an uncontrolled rectifier valve, the uncontrolled rectifier valve comprising a plurality of series diodes connected in series in the arms of a three-phase voltage circuit, characterized in that, The voltage equalization system includes multiple voltage equalization units. Each voltage equalization unit is used to adjust the voltage balance of the series diodes. Each voltage equalization unit includes a voltage regulator module, a first resistor, an energy storage module, a switching module, a second resistor, and a control module. The first terminal of the voltage regulator module is connected to the negative terminal of the series diode. The second terminal of the voltage regulator module is connected to the first terminal of the first resistor and the first terminal of the energy storage module. The second terminal of the energy storage module is connected to the first terminal of the switching module and the first terminal of the second resistor. The positive terminal of the series diode is connected to the second terminal of the first resistor, the second terminal of the switching module, and the second terminal of the second resistor. The control terminal of the switching module is connected to the control module, which is used to control the switching on and off of the switching module. A current-conducting diode is provided between the energy storage module and the second resistor. The positive terminal of the current-conducting diode is connected to the second terminal of the energy storage module, and the negative terminal of the current-conducting diode is connected to the first terminal of the second resistor. The voltage regulator module includes a first capacitor, the capacitance value of which is set according to the voltage value of the voltage signal of the series diode when it is turned off. The first capacitor is used to filter out the overvoltage signal of the series diode. The energy storage module includes a first inductor, the inductance value of which is set according to the overvoltage signal of the series diode. The first inductor is used to store the overvoltage signal and conducts current through the first resistor and the second resistor. The system also includes a PI controller, which performs a difference calculation between the voltage signal of the series diode and the average voltage to obtain a voltage difference value. The input terminal of the PI controller receives the voltage difference value, performs an integral calculation on the voltage difference value, and outputs an integral signal to the control module. The control module is used to control the switching module to turn on and off according to the integral signal, thereby adjusting the equivalent impedance of the series diode.

2. A pressure equalization control method applied to an uncontrolled rectifier valve, characterized in that, This method employs the equalizing system described in claim 1, and the method includes: The voltage signals of each of the series diodes are collected and compared with the set average voltage of the series diodes to calculate the voltage difference; The voltage difference is calculated by PI integration, and the equivalent impedance of the series diode is measured in real time. The equivalent impedance is adjusted to a set average impedance, thereby adjusting the voltage value of the voltage signal; The adjusted voltage signal is subjected to negative feedback, and the voltage difference is continuously reduced.

3. The pressure equalization control method applied to an uncontrolled rectifier valve according to claim 2, characterized in that, Calculate the total impedance of each of the series diodes and the arm voltage value of the three-phase voltage circuit. The ratio of the voltage signal value to the arm voltage value is equal to the ratio of the equivalent impedance to the total impedance.

4. The pressure equalization control method applied to an uncontrolled rectifier valve according to claim 3, characterized in that, The control module adjusts the equivalent impedance by controlling the duty cycle of the switching module.

5. The pressure equalization control method applied to an uncontrolled rectifier valve according to claim 4, characterized in that, The control module uses a DC chopper to adjust the duty cycle of the switching module.

6. The pressure equalization control method applied to an uncontrolled rectifier valve according to claim 2, characterized in that, The average voltage is the average of the steady-state voltages of each of the series diodes when they are turned off.

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