A control method of a power distribution line ice melting device

Abstract

The application discloses a control method of a power distribution line ice melting device, which adopts the power distribution line ice melting device to melt ice, and the ice melting device comprises a parallel side converter, a series side converter, an energy storage capacitor, a parallel side transformer and a series side transformer, the energy storage capacitor is connected between the parallel side converter and the series side converter, the parallel side converter is a three-phase converter, absorbs active power of a fundamental frequency from the power distribution network through the parallel side transformer, the series side converter is a single-phase converter, generates non-fundamental wave current, and injects the non-fundamental wave current into a first end of a line to be melted through a neutral point of the series side transformer to generate Joule heat in the line to be melted to melt ice without power-off operation. Compared with the traditional method, the application can effectively reduce the interference on the power grid, reduce the ice melting cost, and improve the stability and reliability of the system.

Description

Technical Field

[0001] This invention belongs to the field of power transmission line de-icing technology, specifically a control method for a power distribution line uninterrupted de-icing device based on zero-sequence current injection. Background Technology

[0002] With the intensification of global climate change and the increasing frequency of extreme weather events, especially blizzards and low temperatures in winter, overhead power lines often experience icing, seriously affecting the safe and stable operation of the power system. Line icing not only increases the load on conductors and weakens the mechanical strength of towers and conductors, but can also lead to problems such as conductor galloping, insulator flashover, and line breakage, potentially causing widespread power outages in severe cases. Therefore, how to efficiently and continuously solve the problem of power system icing has become a critical technical challenge that the power industry urgently needs to address.

[0003] Traditional de-icing methods mainly include short-circuit de-icing, inductive load regulation, and de-icing equipment based on power electronics technology. While these traditional methods can alleviate icing problems to some extent, they generally suffer from the following drawbacks: 1. Short-circuit de-icing method: This method increases the line current by grounding or phase-to-phase short circuits, thereby utilizing the heat generated by the current to melt ice. This method is inefficient and typically requires individual grounding operations for each phase, increasing operational complexity and potentially affecting the stability and reliability of the entire power grid. Furthermore, this method usually necessitates shutting down some lines, making it unable to meet the continuous power supply demand during peak hours.

[0004] 2. Inductive load regulation method: This method increases the line current by adjusting the inductive load of the power system, thereby achieving ice melting. Although this method avoids direct short circuits, it still requires a relatively high current, and the adjustment process is complex and inflexible, unable to quickly respond to load changes. Therefore, it is not suitable for dealing with sudden extreme weather events.

[0005] 3. De-icing equipment based on power electronics technology: In recent years, de-icing equipment using power electronic devices such as rectifiers, inverters, and multilevel converters has been gradually applied in practice. These devices can provide high current or voltage to heat the conductors and melt the accumulated ice. Although power electronic equipment has achieved certain results in some applications, most devices still require additional control transformers or converters, and their power regulation range is limited, making it difficult to meet the needs of real-time de-icing. Although power electronic technology has shown advantages in improving de-icing efficiency, existing equipment usually relies on shutdown operations and cannot continuously de-ic in place without interrupting the power supply, making it difficult to apply during peak load periods.

[0006] Traditional de-icing methods suffer from low efficiency, require the shutdown of some lines, and are complex to control, thus necessitating a new technological solution. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a control method for a power distribution line uninterrupted de-icing device. The method utilizes a three-phase converter to absorb the base frequency active power of the power grid and injects non-base frequency current into the de-icing line through a single-phase converter to generate Joule heat to achieve de-icing, thereby improving the de-icing efficiency and avoiding the shutdown problem of traditional methods.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a control method for an uninterrupted de-icing device for power distribution lines, wherein the uninterrupted de-icing device includes a parallel-side converter VSC1, a series-side converter VSC2, and an energy storage capacitor C. dc The parallel-side transformer T2 and the series-side transformer T3, and the energy storage capacitor C dc Connected between parallel-side converter VSC1 and series-side converter VSC2; The parallel-side converter VSC1 is a three-phase converter that absorbs the active power of the fundamental frequency from the distribution network through the parallel-side transformer T2; the series-side converter VSC2 is a single-phase converter that generates a non-fundamental current that is injected into the beginning of the line to be melted through the neutral point of the series-side transformer T3, generating Joule heat in the line to be melted for uninterrupted de-icing.

[0009] Furthermore, after flowing to the end of the line to be melted, the non-fundamental current passes through the neutral point of the ground circuit transformer T5 and the ground circuit switch R. G It flows into the ground and forms a loop with the grounding port of the series-connected converter VSC2.

[0010] Furthermore, the equivalent circuit of the ice-melting device in the ice-melting line includes the equivalent impedance of the series-side transformer T3. Z T3 Impedance of de-icing lines Z L Equivalent impedance of ground circuit transformer T5 Z T5 Switching impedance of ground circuit transformer T5 R G Earth loop impedance R g And the current source equivalent to the series-side converter VSC2; The equivalent impedance of the series-side transformer T3 Z T3 Impedance of de-icing lines Z L Equivalent impedance of ground circuit transformer T5 ZT5 Switching impedance R G Earth loop impedance R g A series of current sources are connected in series to form an ice-melting circuit; the current sources output AC voltage. and zero-sequence current Equivalent impedance of series-side transformer T3 Z T3 Zero-sequence current Both the amplitude and phase angle can be varied.

[0011] Furthermore, the AC voltage output by the current source and zero-sequence current The relationship is: (1) The expression for the current flowing through the circuit to be melted is: (2) In the formula, For de-icing current, This refers to the current in the transmission line; From equations (1) and (2), it can be seen that by controlling the zero-sequence current output by the series-side converter... By determining the size and phase, online de-icing of the de-icing line can be performed.

[0012] Furthermore, the parallel-side converter VSC1 is a three-phase bridge voltage source converter.

[0013] Furthermore, the parallel-side converter VSC1 consists of three bridge arms, each containing two IGBT switches (upper and lower). Within the same bridge arm, the emitter of the upper IGBT switch is connected to the collector of the lower IGBT switch, forming the AC output terminal of that bridge arm. The AC side is connected via a grid-side filter inductor Lg and a filter capacitor. C f The converter-side filter inductor L is connected to the power grid; By a filter capacitor C f With an equivalent energy dissipation resistor r Three sets are connected in series, one group in total, and connected to the three phases of the AC output terminal respectively; the energy storage capacitor C is connected between the positive and negative buses on the DC side. dc To maintain voltage stability.

[0014] Furthermore, based on the structure of the parallel-side converter VSC1, the following equation is derived: (3) In the formula, V sa ,V sb , V sc These represent the grid-side voltages respectively. V s The A, B, and C phase components, V sha , V shb , V shc These represent the A, B, and C phase components of the modulation voltage of the three-phase converter, respectively. i sa , i sb , i sc These represent the A, B, and C phase components of the output current of the three-phase converter, respectively. i a , i b , i c This refers to the current in the DC-side filter inductor of the three-phase converter. Perform the following steps on equation (3) Park The transformation yields the mathematical model of the parallel-side converter in the synchronous rotating coordinate system as follows: (4) In the formula, V sd , V sq These represent the grid-side voltages respectively. V s d-axis components, q-axis components, V shd , V shq This represents the d-axis and q-axis components of the modulation voltage of the three-phase converter. i sd , i sq These represent the output current of the three-phase converter. i s d-axis components, q-axis components Indicates the power frequency angular frequency; d-axis component of the modulated voltage of the parallel-side converter V shd With q-axis components V shq They are respectively: (5) The solution obtained from formula (5) V shd , V shqFirst, a three-phase modulation signal is generated through dq / abc coordinate transformation. Then, this signal is used as the modulation wave of SPWM and input to the three-phase converter. By adjusting the on-off timing of the IGBT power devices in the converter, the output of the three-phase converter can finally meet the control target of DC capacitor voltage and AC bus voltage.

[0015] Furthermore, the control strategy of the parallel-side three-phase converter is as follows: active power is absorbed from the transmission line to charge the DC-side energy storage capacitor, maintaining a constant voltage value for the energy storage capacitor to stably supply power to the series-side converter; and the voltage of the parallel-side converter is collected. V s and output current I s For voltage V s Phase-locked loop (PLL) is performed to obtain θ For voltage V s and output current I s Perform dq decomposition to obtain its components along the d and q axes. V sd , V sq , I sd and I sq Then, based on the decomposed d and q axis component signals, the device-level control strategy is executed.

[0016] Furthermore, the d-axis needs to control the voltage of the energy storage capacitor, charge the parallel-side converter, and stabilize the voltage of the energy storage capacitor; the q-axis, according to functional requirements, realizes direct injection of reactive current, and the parallel-side converter is equivalent to a controlled voltage source with adjustable reactive current; realizes reactive power compensation, and compensates the system with a certain amount of inductive or capacitive reactive power; realizes bus voltage regulation, absorbs excess reactive power to reduce bus voltage or compensates for reactive power to raise bus voltage.

[0017] Furthermore, the series-side converter is an H-bridge converter, which is powered by the energy storage capacitor voltage obtained by the rectification of the three-phase converter. By calculating the error between the reference signal and the actual signal of the zero-sequence current, the error is sent to the PID controller for processing. Its output is compared with the triangular carrier wave as a modulation wave to obtain the switching signal that triggers the IGBT on the series-side converter to turn on / off, thereby generating the required zero-sequence current through inversion.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes a three-phase converter to absorb active power at the fundamental frequency from the power grid, and then a single-phase converter generates a non-fundamental current which is injected into the de-icing circuit via the neutral point of a transformer near the series side. Joule heating is generated in the de-icing circuit to achieve uninterrupted de-icing. By controlling the output current of the parallel and series converters, the amplitude and frequency of the de-icing current can be precisely adjusted to ensure the stability and efficiency of the de-icing process.

[0019] This invention not only improves the efficiency of de-icing but also avoids the downtime problem of traditional methods. It is also highly adaptable and particularly suitable for the power system operation needs under extreme weather conditions.

[0020] In addition to enabling online ice melting, this invention also achieves functions such as harmonic voltage suppression and improved power quality. Attached Figure Description

[0021] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a topology diagram of the uninterrupted power supply de-icing device for power distribution lines according to the present invention; Figure 2 This is the equivalent circuit diagram of the power distribution line uninterrupted de-icing device of the present invention in the line to be de-iced; Figure 3 This is a topology diagram of the parallel-side converter of the present invention; Figure 4 This is a control strategy diagram for the parallel-side converter of the present invention; Figure 5 This is a topology diagram of the series-side converter of the present invention; Figure 6 This is a control strategy diagram for the series-side converter of the present invention; Figure 7 This is an overall diagram of the zero-sequence current I2 in the simulation test of this invention; Figure 8 This is a partial view of the zero-sequence current I2 in the simulation test of this invention; Figure 9 This is a comparison diagram of the single-phase fundamental current and single-phase zero-sequence current of the circuit to be melted in the simulation test of this invention; Figure 10 DC voltage in the simulation test of this invention V dc Change diagram. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer through the following description. It should be noted that the accompanying drawings are in a simplified schematic form, and the proportions shown are not precise; they are only for auxiliary illustration and are intended to help understand the embodiments of the present invention. Please refer to the accompanying drawings for a clearer demonstration of the purpose, features, and advantages of the present invention. It should be pointed out that the structures, proportions, sizes, etc., shown in the accompanying drawings are only for illustrative purposes and do not limit the specific conditions of the embodiments of the present invention; therefore, they do not have substantial technical significance. Any modifications to the structure, adjustments to the proportions, or changes in the dimensions, without affecting the function and purpose achieved by the present invention, should be considered within the scope of the technical solution of the present invention.

[0024] This embodiment describes a control method for an uninterrupted de-icing device for power distribution lines. It utilizes a three-phase converter to absorb active power at the fundamental frequency from the power grid, and then a single-phase converter generates a non-fundamental current which is injected into the de-icing line via the neutral point of a transformer near the series side. This generates Joule heat in the de-icing line, achieving uninterrupted de-icing. By controlling the output current of the parallel and series converters, the amplitude and frequency of the de-icing current can be precisely adjusted to ensure the stability and efficiency of the de-icing process and avoid the downtime problems of traditional methods.

[0025] like Figure 1 As shown, the uninterrupted power supply de-icing device for the power distribution line consists of a parallel-side converter VSC1, a series-side converter VSC2, and an energy storage capacitor C. dc Parallel-side transformer T2, series-side transformer T3, user isolation transformer T4, ground circuit transformer T5, and ground circuit switch R G Composition, the energy storage capacitor C dc Connected between parallel-side converter VSC1 and series-side converter VSC2; The parallel-side converter VSC1 is a three-phase converter that absorbs active power at the fundamental frequency from the distribution network via the parallel-side transformer T2. The series-side converter VSC2 is a single-phase converter that generates a non-fundamental current, which is injected into the beginning of the line to be melted via the neutral point of the Y / Δ connected series-side transformer T3. This generates Joule heating in the line to be melted, enabling uninterrupted ice melting. After flowing to the end of the line, the non-fundamental current passes through the neutral point of the ground loop transformer T5 and the ground loop switch R. G It flows into the ground and forms a loop with the grounding port Out_N of the series-side converter VSC2.

[0026] like Figure 2 As shown, the equivalent circuit of the uninterruptible ice-melting device in the ice-melting line is represented by the equivalent impedance of the series-side transformer T3. Z T3Impedance of de-icing lines Z L Equivalent impedance of ground circuit transformer T5 Z T5 Switching impedance of transformer T5 R G Earth loop impedance R g It consists of a current source equivalent to the series-connected converter VSC2.

[0027] The equivalent impedance of the series-side transformer T3 Z T3 Impedance of de-icing lines Z L Equivalent impedance of ground circuit transformer T5 Z T5 Switching impedance R G Earth loop impedance R g A series of current sources are connected in series to form an ice-melting circuit; the current sources output AC voltage. and zero-sequence current Equivalent impedance of series-side transformer T3 Z T3 Zero-sequence current Both the amplitude and phase angle can be varied.

[0028] Depend on Figure 2 It can be seen that the AC voltage output by the current source and zero-sequence current The relationship is: (1) The expression for the current flowing through the circuit to be melted is: (2) In the formula, For de-icing current, This refers to the current in the transmission line; From equations (1) and (2), it can be seen that by controlling the zero-sequence current output by the series-side converter... By determining the size and phase, online de-icing of the de-icing line can be performed.

[0029] The parallel-side converter VSC1 is a three-phase bridge voltage source converter, such as... Figure 3 As shown, the parallel-side converter VSC1 consists of three bridge arms, each containing two IGBT switches, one upper and one lower. In the same bridge arm, the emitter of the upper IGBT switch is connected to the collector of the lower IGBT switch, forming the AC output terminal of the bridge arm. The AC side is connected to the power grid through the grid-side filter inductor Lg, the filter capacitor Cf, and the converter-side filter inductor L. By a filter capacitor C f With an equivalent energy dissipation resistor r Three sets are connected in series, one group in total, and connected to the three phases of the AC output terminal respectively; the energy storage capacitor C is connected between the positive and negative buses on the DC side. dc To maintain voltage stability.

[0030] Figure 3 middle, V dcsh This represents the voltage across the energy storage capacitor. V sh This represents the modulation voltage of the three-phase converter. V s Indicates the grid-side voltage. i s This represents the grid-side current.

[0031] Due to resistance r The flow is very large, and it is assumed that the current flows through the filter capacitor. C f current i c =0 (i.e.) i ca = i cb = i cc If =0), then it can be obtained from Figure 3 The following equation is derived from the parallel-side converter VSC1 topology: (3) In the formula, V sa , V sb , V sc These represent the grid-side voltages respectively. V s The A, B, and C phase components, V sha , V shb , V shc These represent the A, B, and C phase components of the modulation voltage of the three-phase converter, respectively. i sa , i sb , i sc These represent the A, B, and C phase components of the output current of the three-phase converter, respectively. i a , i b , ic This represents the current in the DC-side filter inductor of the three-phase converter.

[0032] Perform on equation (3) Park The transformation yields the mathematical model of the parallel-side converter in the synchronous rotating coordinate system as follows: (4) In the formula, V sd , V sq These represent the grid-side voltages respectively. V s d-axis components, q-axis components, V shd , V shq This represents the d-axis and q-axis components of the modulation voltage of the three-phase converter. i sd , i sq These represent the output current of the three-phase converter. i s d-axis components, q-axis components Indicates the power frequency angular frequency; d-axis component of the modulated voltage of the parallel-side converter V shd With q-axis components V shq They are respectively: (5) The solution obtained from formula (5) V shd , V shq First, a three-phase modulation signal is generated through dq / abc coordinate transformation. Then, this signal is used as the modulation wave of SPWM and input to the three-phase converter. By adjusting the on-off timing of the IGBT power devices in the converter, the output of the three-phase converter can finally meet the control target of DC capacitor voltage and AC bus voltage.

[0033] From the above formulas, the control strategy for the parallel-side converter of the ice-melting device can be obtained as follows: Figure 4 As shown, Figure 4 middle V dcshref , V sref These are the reference values ​​for DC capacitor voltage and AC bus voltage, respectively. i sdref , i sqref These are the reference values ​​for the d-axis and q-axis currents, respectively. V s This is the effective value of the AC bus voltage.

[0034] The control strategy for the parallel-side three-phase converter is as follows: It absorbs active power from the transmission line to charge the DC-side energy storage capacitor, maintaining a constant voltage value for the energy storage capacitor to stably supply power to the series-side converter. This is achieved by collecting the voltage of the parallel-side converter. V s and output current I s For voltage V s Phase-locked loop (PLL) is performed to obtain θ For voltage V s and output current I s Perform dq decomposition to obtain its components along the d and q axes. V sd , V sq , I sd and I sq Then, based on the decomposed d and q axis component signals, the device-level control strategy is executed.

[0035] The d-axis controls the voltage of the energy storage capacitor, charges the parallel-side converter, and stabilizes the voltage of the energy storage capacitor. The q-axis, according to functional requirements, enables direct injection of reactive current, making the parallel-side converter equivalent to a controlled voltage source with adjustable reactive current. It also enables reactive power compensation, compensating the system with a certain amount of inductive or capacitive reactive power. Furthermore, it enables bus voltage regulation, absorbing excess reactive power to reduce the bus voltage or compensating for reactive power to raise the bus voltage.

[0036] The series-side converter is an H-bridge converter, and its topology is as follows: Figure 5 As shown, its control strategy is as follows: Figure 6 As shown, the energy storage capacitor voltage obtained by the rectification of the three-phase converter is used for power supply. The error between the reference signal and the actual signal of the zero-sequence current is calculated and sent to the PID controller for processing. Its output is compared with the triangular carrier wave as a modulation wave to obtain the switching signal that triggers the IGBT on the series-side converter to turn on / off, thereby generating the required zero-sequence current by inverter. Figure 6 In I 2ref for I The reference value is 2.

[0037] The invention will now be described in further detail with reference to simulation examples.

[0038] The simulation test procedure for a control method of an uninterrupted power supply de-icing device for power distribution lines is set as follows: (1) The total simulation duration is 3s, and the parallel-side converter is connected to the line at 0.1s. (2) The parallel-side converter is put into operation at 0.5s; (3) At time 1s, the series-connected converter injects non-fundamental current into the first end of the line to be melted.

[0039] like Figure 7 , 8 As shown, at 1 second, the effective value of the zero-sequence current given by the series-side converter is 1.5kA, and the frequency is 150Hz. The zero-sequence current quickly responds to the given value after 0.17 seconds and remains stable. This is equivalent to injecting an effective value of 0.5kA and a frequency of 150Hz de-icing current I1 into each phase of the line to be de-iced.

[0040] like Figure 9 As shown, I13f is the effective value of the zero-sequence current of a single phase of the line to be melted. When the series-side converter injects harmonic current into the line to be melted, it rises to 0.5kA and remains stable. I11f is the effective value of the fundamental current of a single phase of the line to be melted, which remains basically stable after the line is turned on.

[0041] like Figure 10 As shown, at 0.1s, the parallel-side converter connects to the transmission line and begins to charge the energy storage capacitor, causing the DC voltage to rise. At this time, the parallel-side converter absorbs active power from the transmission line. At 0.5s, the parallel-side converter provides a DC voltage of 14KV. The DC voltage rises to the given value after 0.12s and remains stable after a small fluctuation of 0.1s when VSC2 generates zero-sequence current at 1s.

[0042] The above description is only 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 within the protection scope of the present invention.

Claims

1. A control method for an uninterrupted de-icing device for power distribution lines, characterized in that, The uninterruptible ice-melting device includes a parallel-side converter VSC1, a series-side converter VSC2, and an energy storage capacitor C. dc The parallel-side transformer T2 and the series-side transformer T3, and the energy storage capacitor C dc Connected between parallel-side converter VSC1 and series-side converter VSC2; The parallel-side converter VSC1 is a three-phase converter that absorbs the active power of the fundamental frequency from the distribution network through the parallel-side transformer T2; the series-side converter VSC2 is a single-phase converter that generates a non-fundamental current that is injected into the beginning of the line to be melted through the neutral point of the series-side transformer T3, generating Joule heat in the line to be melted for uninterrupted de-icing.

2. The control method for the uninterrupted de-icing device for power distribution lines according to claim 1, characterized in that, The non-fundamental current flows through the line to be melted to the end, then through the neutral point of the ground circuit transformer T5 and the ground circuit switch R. G It flows into the ground and forms a loop with the grounding port of the series-connected converter VSC2.

3. The control method for the uninterrupted de-icing device for power distribution lines according to claim 2, characterized in that, The equivalent circuit of the ice-melting device in the ice-melting line includes the equivalent impedance of the series-side transformer T3. Z T3 Impedance of de-icing lines Z L Equivalent impedance of ground circuit transformer T5 Z T5 Switching impedance of transformer T5 R G Earth loop impedance R g And the current source equivalent to the series-side converter VSC2; The equivalent impedance of the series-side transformer T3 Z T3 Impedance of de-icing lines Z L Equivalent impedance of ground circuit transformer T5 Z T5 Switching impedance R G Earth loop impedance R g A series of current sources are connected in series to form an ice-melting circuit; the current sources output AC voltage. and zero-sequence current Equivalent impedance of series-side transformer T3 Z T3 Zero-sequence current Both the amplitude and phase angle can be varied.

4. The control method for the uninterrupted de-icing device for power distribution lines according to claim 3, characterized in that, AC voltage output by the current source and zero-sequence current The relationship is: (1) The expression for the current flowing through the circuit to be melted is: (2) In the formula, For de-icing current, This refers to the current in the transmission line; From equations (1) and (2), it can be seen that by controlling the zero-sequence current output by the series-side converter... By determining the size and phase, online de-icing of the de-icing line can be performed.

5. The control method for the uninterrupted de-icing device for power distribution lines according to claim 1, characterized in that, The parallel-side converter VSC1 is a three-phase bridge voltage source converter.

6. The control method for the uninterrupted de-icing device for power distribution lines according to claim 5, characterized in that, The parallel-side converter VSC1 consists of three bridge arms, each containing two IGBT switches (upper and lower). Within the same bridge arm, the emitter of the upper IGBT switch is connected to the collector of the lower IGBT switch, forming the AC output terminal of that bridge arm. The AC side is connected to the grid-side filter inductor Lg and filter capacitor C. f The converter-side filter inductor L is connected to the power grid; By a filter capacitor C f With an equivalent energy dissipation resistor r Three sets are connected in series, one group in total, and connected to the three phases of the AC output terminal respectively; the energy storage capacitor C is connected between the positive and negative buses on the DC side. dc To maintain voltage stability.

7. The control method for the uninterrupted de-icing device for power distribution lines according to claim 6, characterized in that, The following formula is derived from the structure of the parallel-side converter VSC1: (3) In the formula, V sa , V sb , V sc These represent the grid-side voltages respectively. V s The A, B, and C phase components, V sha , V shb , V shc These represent the A, B, and C phase components of the modulation voltage of the three-phase converter, respectively. i sa , i sb , i sc These represent the A, B, and C phase components of the output current of the three-phase converter, respectively. i a , i b , i c This refers to the current in the DC-side filter inductor of the three-phase converter. Perform on equation (3) Park The transformation yields the mathematical model of the parallel-side converter in the synchronous rotating coordinate system as follows: (4) In the formula, V sd , V sq These represent the grid-side voltages respectively. V s d-axis components, q-axis components, V shd , V shq This represents the d-axis and q-axis components of the modulation voltage of the three-phase converter. i sd , i sq These represent the output current of the three-phase converter. i s d-axis components, q-axis components, Indicates the power frequency angular frequency; d-axis component of the modulated voltage of the parallel-side converter V shd With q-axis components V shq They are respectively: (5) The solution obtained from formula (5) V shd , V shq First, a three-phase modulation signal is generated through dq / abc coordinate transformation. Then, this signal is used as the modulation wave of SPWM and input to the three-phase converter. By adjusting the on-off timing of the IGBT power devices in the converter, the output of the three-phase converter can finally meet the control target of DC capacitor voltage and AC bus voltage.

8. The control method for the uninterrupted de-icing device for power distribution lines according to claim 7, characterized in that, The control strategy for the parallel-side three-phase converter is as follows: It absorbs active power from the transmission line to charge the DC-side energy storage capacitor, maintaining a constant voltage value for the energy storage capacitor to stably supply power to the series-side converter. This is achieved by collecting the voltage of the parallel-side converter. V s and output current I s For voltage V s Phase-locked loop (PLL) is performed to obtain θ For voltage V s and output current I s Perform dq decomposition to obtain its components along the d and q axes. V sd , V sq , I sd and I sq Then, based on the decomposed d and q axis component signals, the device-level control strategy is executed.

9. The control method for the uninterrupted de-icing device for power distribution lines according to claim 8, characterized in that, The d-axis needs to control the voltage of the energy storage capacitor, charge the parallel-side converter, and stabilize the voltage of the energy storage capacitor. The q-axis, according to functional requirements, realizes direct injection of reactive current, and the parallel-side converter is equivalent to a controlled voltage source with adjustable reactive current. It realizes reactive power compensation, compensating the system with a certain amount of inductive or capacitive reactive power. It realizes bus voltage regulation, absorbing excess reactive power to reduce the bus voltage or compensating for reactive power to raise the bus voltage.

10. The control method for the uninterrupted de-icing device for power distribution lines according to claim 1, characterized in that, The series-side converter is an H-bridge converter, which is powered by the energy storage capacitor voltage obtained by the rectification of the three-phase converter. By calculating the error between the reference signal and the actual signal of the zero-sequence current, the error is sent to the PID controller for processing. The output is used as a modulation wave and compared with the triangular carrier wave to obtain the switching signal that triggers the IGBT on the series-side converter to turn on / off, thereby generating the required zero-sequence current through inversion.

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