A distribution network step-up and step-down non-interference switching method and system

Abstract

The application relates to the technical field of power distribution network operation and maintenance, and particularly discloses a distribution network step-up and step-down disturbance-free switching method and system, which comprises the following steps: performing out-of-limit discrimination on the effective value of the voltage of the power distribution network grid side port, combining with current operation mode logical comparison to generate a target operation mode instruction; fusing the inductance current direction, amplitude and port voltage phase difference sequence to construct a switching window pre-judgment sequence and determine an optimal switching time window; generating a bypass switch pre-action time sequence matrix according to the target instruction in the window, calculating a pre-switching duty cycle reference value, and pre-adjusting the AC / AC converter bidirectional switch duty cycle; completing the switching of the switch on-off according to the time sequence in the zero current crossing interval, and smoothly transitioning the duty cycle to the target steady-state duty cycle according to a preset slope after switching; and compensating the duty cycle in real time through overload side voltage deviation proportional regulation to stabilize the load side voltage in the qualified interval; and the application can improve the smoothness, power supply reliability and voltage regulation precision of distribution network voltage regulation switching.

Description

Technical Field

[0001] This invention relates to the field of power distribution network operation and maintenance technology, and in particular to a method and system for seamless switching of step-up and step-down voltage in power distribution networks. Background Technology

[0002] Currently, step-up and step-down voltage regulators in power distribution networks often use a bypass switch to directly switch on and off during operation mode switching. This switching process easily generates significant voltage fluctuations and current surges, causing a sharp drop in power quality on the load side and making it difficult to meet the high stability requirements of power consumption scenarios. Furthermore, existing switching strategies lack precise prediction of switching timing, and switching actions often occur during the peak inductor current range. This significantly increases the switching stress on the switching devices, shortening their lifespan and easily triggering transient disturbances on the grid side, adversely affecting the operational stability of the power distribution network.

[0003] In existing voltage regulation switching control systems, the collaborative control logic between the AC / AC converter and the bypass switching switch is relatively simple, generally lacking a pre-switching state adjustment stage. The sudden change in the converter's duty cycle before and after switching further amplifies the voltage overshoot and drop. In addition, conventional voltage regulation control relies solely on a fixed steady-state duty cycle to maintain the output voltage, without setting a real-time deviation compensation mechanism. When the load fluctuates or the grid parameters change, the load-side voltage is prone to deviating from the qualified range, resulting in significant limitations in voltage regulation accuracy and dynamic response capability. Summary of the Invention

[0004] In view of the above problems, the purpose of this invention is to provide a method and system for seamless switching of step-up and step-down voltage in distribution networks, so as to solve the problems of unreasonable selection of switching timing, poor coordination between AC / AC converter and bypass switch, severe transient voltage and current disturbances during switching, insufficient steady-state voltage regulation accuracy, and excessive operating stress of devices in the existing step-up and step-down voltage switching process.

[0005] This invention provides a method for a distribution network step-up / step-down seamless switching switch, comprising: Step 1: Determine if the effective value of the voltage at the grid-side port in the distribution network exceeds the limit, and logically compare the obtained voltage over-limit status flag with the current operating mode of the distribution network to generate the target operating mode command; Step 2: In the distribution network, the direction and amplitude of the inductor current and the phase difference between the port voltages of the grid side and the load side are fused and sorted to construct a switching window prediction sequence and determine the optimal switching time window; Step 3: Within the optimal switching time window, according to the target operation mode instruction, arrange the pre-conduction states of the bypass switching switches in the distribution network into a switch pre-action timing matrix; Step 4: Calculate the pre-switching duty cycle reference value based on the voltage regulation ratio corresponding to the target operating mode command, and adjust the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value. Step 5: When the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window, according to the switch pre-action timing matrix, the on / off switching of each branch switch in the bypass switching switch is performed, and after the switching is completed, the duty cycle of the bidirectional switching tube is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to the preset slope, so as to obtain the voltage regulation operation state after the disturbanceless switching. Step 6: In the voltage regulation operation state after the disturbance-free switching, the voltage deviation between the load side port voltage signal and the preset voltage reference value is proportionally adjusted and superimposed on the target steady-state duty cycle to generate a real-time duty cycle command and output it to the bidirectional switching transistor, so that the load side port voltage is stabilized within the preset voltage qualified range.

[0006] Preferably, the process of determining the effective value of the grid-side port voltage in the distribution network to exceed the limit, and logically comparing the obtained voltage over-limit status identifier with the current operating mode of the distribution network to generate a target operating mode instruction, is as follows: The root mean square operation is performed on each sampled value of the grid-side port voltage within one power frequency cycle to obtain the effective value of the grid-side port voltage. When the effective value is greater than the preset upper voltage threshold, a voltage exceeding the upper limit is generated; when the effective value is less than the preset lower voltage threshold, a voltage exceeding the lower limit is generated; when the effective value is between the preset lower voltage threshold and the preset upper voltage threshold, a voltage normal is generated, thus obtaining the voltage exceeding the limit status of the grid-side port voltage. The voltage over-limit status indicator is logically combined with the current operating mode indicator of the distribution network for judgment. The current operating mode indicator includes boost mode, buck mode and bypass direct mode. Use the generated mode instruction corresponding to the current running mode identifier as the target running mode instruction.

[0007] Preferably, the process of logically combining and judging the voltage over-limit status indicator with the current operating mode indicator of the distribution network is as follows: When the voltage over-limit status is indicated by the voltage over-limit flag and the current operating mode is not buck mode, a buck mode command is generated. When the voltage over-limit status is marked as the voltage under-limit status and the current operating mode is not boost mode, a boost mode command is generated. When the voltage over-limit status indicator is changed to the voltage normal status indicator, or when the voltage over-limit status indicator matches the current operating mode indicator, a command to maintain the current mode is generated.

[0008] Preferably, in the distribution network, the direction and amplitude of the inductor current, as well as the phase difference between the port voltages on the grid side and the load side, are fused and sorted to construct a switching window prediction sequence and determine the optimal switching time window. The process is as follows: The instantaneous values ​​of the inductor current at multiple consecutive sampling times are obtained, the direction of the inductor current is determined according to the positive and negative polarities of the instantaneous values, and the absolute value of the instantaneous values ​​is taken as the amplitude of the inductor current. Calculate the time difference between the port voltages of the grid side and the load side in the distribution network at the zero crossing moment, and take the ratio between the time difference and the power frequency period of the distribution network as the phase difference between the port voltages of the grid side and the load side. The current inductor current direction, current amplitude, and port voltage phase difference are weighted and fused according to preset weighting coefficients to obtain the switching window evaluation value of the distribution network at the current moment. Based on the current time, slide forward a preset time window length, calculate the switching window evaluation value corresponding to each time within the preset time window length in turn, and sort each time according to the switching window evaluation value from best to worst to obtain the switching window prediction sequence. The optimal switching time window is obtained by selecting the time with the best evaluation value from the switching window prediction sequence as the center time and expanding outward with a preset width centered on the center time.

[0009] Preferably, within the optimal switching time window, the pre-conduction states of the bypass switching switches in the distribution network are arranged into a switch pre-action timing matrix according to the target operation mode instruction. The process is as follows: Read the current on / off status of each branch switch in the bypass switching switch in the distribution network; Query the pre-conduction target state of each branch switch corresponding to the target operation mode command from the preset switch state mapping table; Compare the current on / off state of each branch switch with the target state of pre-conduction to determine the target branch switch whose state needs to be changed and the corresponding target state. According to the preset switching sequence within the optimal switching time window, the target branch switches and their corresponding target states are arranged in the order of action to generate a switching action sequence. The switching action sequence is encoded into a binary matrix with each branch switch as the row and the time tick as the column, thus obtaining the switch pre-action timing matrix.

[0010] Preferably, the process of calculating the pre-switching duty cycle reference value based on the voltage regulation ratio corresponding to the target operating mode command, and adjusting the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value, is as follows: Decode the target operating mode command to identify the voltage regulation direction and voltage regulation amplitude corresponding to the target operating mode command. The voltage regulation direction includes either the voltage boosting direction or the voltage bucking direction, and the voltage regulation amplitude includes the voltage regulation ratio value corresponding to the target operating mode command. Calculate the pre-switching duty cycle reference value based on the voltage regulation direction and voltage regulation amplitude; The difference between the current duty cycle of the bidirectional switching transistor inside the AC / AC converter and the reference value of the pre-switching duty cycle is used as the duty cycle adjustment deviation. Based on the positive and negative directions of the duty cycle adjustment deviation, the duty cycle adjustment direction of the bidirectional switch is determined, and the duty cycle of the bidirectional switch is gradually changed according to the preset single adjustment step size until the duty cycle of the bidirectional switch reaches the pre-switching duty cycle reference value.

[0011] Preferably, the process of calculating the pre-switching duty cycle reference value based on the voltage regulation direction and voltage regulation amplitude is as follows: Obtain the high-voltage side port voltage sampling value and the low-voltage side port voltage sampling value inside the AC / AC converter; Based on the voltage regulation direction, one of the voltage sampling values ​​at the high-voltage side port and the low-voltage side port is determined as the reference voltage, and the other is determined as the target voltage. When the voltage regulation direction is the boost direction, the high voltage side port voltage sampling value is used as the reference voltage and the low voltage side port voltage sampling value is used as the target voltage. When the voltage regulation direction is the voltage reduction direction, the low-voltage side port voltage sampling value is used as the reference voltage and the high-voltage side port voltage sampling value is used as the target voltage. The ratio of the target voltage to the reference voltage is used as the voltage transfer ratio, and divided by the equivalent gain coefficient of the AC / AC converter in the current operating state, to obtain the pre-switching duty cycle reference value.

[0012] Preferably, when the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window, the on / off switching of each branch switch in the bypass switching switch is performed according to the switch pre-action timing matrix. After the switching is completed, the duty cycle of the bidirectional switching transistor is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to a preset slope, so as to obtain the voltage regulation operation state after the disturbanceless switching. The process is as follows: The instantaneous value of the inductor current in the distribution network is compared with the preset zero current threshold. When the instantaneous value of the inductor current is less than or equal to the preset zero current threshold, it is determined that the inductor current has entered the zero current state, and the duration of the inductor current in the zero current state is recorded. When the duration is greater than or equal to the preset duration threshold, the inductor current is determined to be in the zero current crossover interval corresponding to the optimal switching time window. Within the zero current crossing range, the action sequence of each branch switch in the pre-action timing matrix of the switch is analyzed, and the on / off control signal of each branch switch is output sequentially according to the action order in the action sequence of each branch switch, so as to complete the on / off switching of all branch switches to be operated in the bypass switching switch. After detecting that all the switch to be operated has completed the on / off switching, the difference between the target steady-state duty cycle corresponding to the target operating mode command and the pre-switching duty cycle reference value is divided by the preset number of adjustment steps to obtain the single-step adjustment amount. According to the preset slope, the duty cycle of the bidirectional switching transistor is increased by a single-step adjustment amount in every two adjacent switching cycles until the duty cycle of the bidirectional switching transistor reaches the target steady-state duty cycle, thus obtaining the voltage regulation operation state after disturbance-free switching.

[0013] Preferably, in the voltage regulation operation state after the disturbance-free switching, the voltage deviation between the load-side port voltage signal and the preset voltage reference value is proportionally adjusted and then superimposed on the target steady-state duty cycle to generate a real-time duty cycle command and output to the bidirectional switching transistor, so that the load-side port voltage is stabilized within the preset qualified voltage range. The process is as follows: The instantaneous voltage values ​​of the load-side port voltage are continuously collected at multiple sampling times, and the instantaneous voltage values ​​at multiple sampling times are subjected to mean filtering to obtain the real-time effective voltage value of the load-side port voltage. The duty cycle compensation amount is obtained by multiplying the voltage deviation between the real-time effective voltage value and the preset voltage reference value by the preset proportional gain coefficient. The duty cycle compensation is superimposed on the target steady-state duty cycle of the distribution network at the current moment to obtain the real-time duty cycle command. The real-time duty cycle command is converted into a pulse width modulation signal and output to the drive terminal of the bidirectional switch to adjust the conduction duty cycle of the bidirectional switch so that the real-time effective value of the load-side port voltage approaches the preset voltage reference value.

[0014] The present invention also provides a distribution network step-up / step-down seamless switching system, the system comprising: The operation mode decision module is used to determine the over-limit of the effective value of the voltage at the grid side port in the distribution network, and to logically compare the obtained voltage over-limit status identifier with the current operation mode of the distribution network to generate the target operation mode instruction; The switching window prediction module is used to integrate and sort the direction and amplitude of inductor current and the phase difference between the port voltages of the grid side and the load side in the distribution network, construct the switching window prediction sequence, and determine the optimal switching time window. The switch timing arrangement module is used to arrange the pre-conduction states of the bypass switching switches in the distribution network into a switch pre-action timing matrix according to the target operation mode instruction within the optimal switching time window; The duty cycle pre-adjustment module is used to calculate the pre-switching duty cycle reference value based on the voltage adjustment ratio corresponding to the target operating mode command, and adjust the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value. The bumpless switching execution module is used to perform on / off switching on each branch switch in the bypass switching switch according to the switch pre-action timing matrix when the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window. After the switching is completed, the duty cycle of the bidirectional switching transistor is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to the preset slope, so as to obtain the voltage regulation operation state after bumpless switching. The real-time voltage regulation control module is used to, in the voltage regulation operation state after disturbance-free switching, to proportionally adjust the voltage deviation between the load-side port voltage signal and the preset voltage reference value and add it to the target steady-state duty cycle, generate a real-time duty cycle command and output it to the bidirectional switching transistor, so that the load-side port voltage is stabilized within the preset voltage qualified range.

[0015] As can be seen from the above technical solution, the present invention provides a distribution network step-up / step-down seamless switching method and system. By judging the voltage of the grid side port and comparing it with the current operating mode logic, a precise target operating mode command can be generated. By combining the inductor current direction, amplitude and port voltage phase difference to construct a switching window prediction sequence, the optimal switching time window can be accurately determined. With the adjustment of the switch pre-action timing matrix and the pre-switching duty cycle reference value, the bypass switch switching is completed in the zero current crossing range, and the switch smoothly transitions to the target steady-state duty cycle with a preset slope. This effectively eliminates voltage surges and current disturbances during the switching process, reduces the switching stress of the switching devices, and compensates the duty cycle in real time by adjusting the load side voltage deviation ratio, so that the load side voltage is stabilized within the qualified range. This comprehensively improves the smoothness of distribution network voltage regulation switching, power supply reliability and voltage regulation accuracy. Attached Figure Description

[0016] Other objects and results of the invention will become more apparent and readily understood by referring to the following description taken in conjunction with the accompanying drawings, and with a more complete understanding of the invention. In the drawings: Figure 1 This is a flowchart illustrating a method for seamless switching of step-up and step-down voltage in a distribution network according to an embodiment of the present invention. Figure 2 This is a functional block diagram of a power distribution network step-up / step-down seamless switching system according to an embodiment of the present invention. Detailed Implementation

[0017] The existing distribution network buck-boost switching process suffers from unreasonable timing selection, poor coordination between AC / AC converters and bypass switches, severe transient voltage and current disturbances during switching, insufficient steady-state voltage regulation accuracy, and excessive operating stress on devices.

[0018] To address the aforementioned problems, this invention provides a method and system for seamless switching of step-up and step-down voltage in power distribution networks. The specific embodiments of this invention will be described in detail below with reference to the accompanying drawings.

[0019] To illustrate the bumpless switching method and system for power distribution network step-up / step-down switching provided by this invention... Figure 1 An exemplary illustration is provided for a distribution network step-up / step-down seamless switching method according to an embodiment of the present invention; Figure 2 An exemplary illustration of a distribution network step-up / step-down seamless switching system according to an embodiment of the present invention is provided.

[0020] The following description of exemplary embodiments is merely illustrative and is in no way intended to limit the invention or its application or use. Techniques and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques and equipment should be considered part of the specification.

[0021] Reference Figure 1 The diagram shown is a flowchart illustrating a method for seamless switching of distribution network step-up / step-down voltage according to an embodiment of the present invention. In this embodiment, the method includes: Step 1: Determine if the effective value of the voltage at the grid-side port in the distribution network exceeds the limit, and logically compare the obtained voltage over-limit status flag with the current operating mode of the distribution network to generate the target operating mode command; In this embodiment of the invention, the process of determining the over-limit status of the effective value of the grid-side port voltage in the distribution network, logically comparing the obtained voltage over-limit status identifier with the current operating mode of the distribution network, and generating a target operating mode instruction is as follows: The root mean square operation is performed on each sampled value of the grid-side port voltage within one power frequency cycle to obtain the effective value of the grid-side port voltage. When the effective value is greater than the preset upper voltage threshold, a voltage exceeding the upper limit is generated; when the effective value is less than the preset lower voltage threshold, a voltage exceeding the lower limit is generated; when the effective value is between the preset lower voltage threshold and the preset upper voltage threshold, a voltage normal is generated, thus obtaining the voltage exceeding the limit status of the grid-side port voltage. The voltage over-limit status indicator is logically combined with the current operating mode indicator of the distribution network for judgment. The current operating mode indicator includes boost mode, buck mode and bypass direct mode. Use the generated mode instruction corresponding to the current running mode identifier as the target running mode instruction.

[0022] The process of logically combining the voltage over-limit status identifier with the current operating mode identifier of the distribution network for discrimination is as follows: When the voltage over-limit status is indicated by the voltage over-limit flag and the current operating mode is not buck mode, a buck mode command is generated. When the voltage over-limit status is marked as the voltage under-limit status and the current operating mode is not boost mode, a boost mode command is generated. When the voltage over-limit status indicator is changed to the voltage normal status indicator, or when the voltage over-limit status indicator matches the current operating mode indicator, a command to maintain the current mode is generated.

[0023] The continuous time-domain waveform of the grid-side port voltage in the distribution network within one power frequency cycle is sampled at equal intervals to obtain multiple instantaneous voltage sample values ​​arranged chronologically within that power frequency cycle. The square of each instantaneous voltage sample value is then calculated, and all squared values ​​are summed to obtain the sum of squares. This sum of squares is divided by the total number of sample points in the sampling sequence to obtain the mean square value. Finally, the square root of the mean square value is taken to obtain the effective value of the grid-side port voltage.

[0024] The effective value of the grid-side port voltage is compared with a preset upper voltage threshold. If the effective value is greater than the preset upper voltage threshold, a voltage exceeding the upper limit is generated. The effective value of the grid-side port voltage is compared with a preset lower voltage threshold. If the effective value is less than the preset lower voltage threshold, a voltage exceeding the lower limit is generated. If the effective value is greater than or equal to the preset lower voltage threshold and less than or equal to the preset upper voltage threshold, a voltage normal is generated. These three comparison operations uniquely generate one of the three indicators—a voltage exceeding the upper limit, a voltage exceeding the lower limit, or a voltage normal—based on the actual magnitude of the effective value. This unique indicator is the voltage exceeding-limit status indicator for the grid-side port voltage.

[0025] Read the current operating mode identifier corresponding to the current operating status of the distribution network. The current operating mode identifier is one of three: boost mode identifier, buck mode identifier, or bypass direct connection mode identifier. Logically combine the voltage over-limit status identifier with the current operating mode identifier for discrimination, following these rules: When the voltage over-limit status is indicated by the voltage over-limit indicator and the current operating mode is not the step-down mode indicator, the non-step-down mode indicator is specifically the step-up mode indicator or the bypass direct-through mode indicator. In this case, the judgment result is that the distribution network needs to be switched to step-down operation, so a step-down mode command is generated. When the voltage over-limit status is identified as the voltage under-limit status and the current operating mode is not the boost mode status, specifically the buck mode status or the bypass direct mode status, the determination result is that the distribution network needs to be switched to boost operation, and therefore a boost mode command is generated. When the voltage over-limit status is marked as the voltage normal status, regardless of the current operating mode, the judgment result is that the distribution network does not need to perform any voltage boosting or bucking adjustments at present, and therefore a command to maintain the current mode is generated. When the voltage over-limit status is identified as the voltage over-limit status and the current operating mode is identified as the step-down mode, the judgment result is that the distribution network is currently in a step-down operating state and there is no need to switch again. Therefore, a command to maintain the current mode is generated. When the voltage over-limit status is identified as the voltage under-limit status and the current operating mode is identified as the boost mode, the judgment result is that the distribution network is currently in boost operation mode and there is no need to switch again. Therefore, a command to maintain the current mode is generated. When the voltage over-limit status is marked as normal voltage and the current operating mode is marked as bypass direct mode, the judgment result is that the distribution network is currently in a direct state and the voltage is normal, requiring no adjustment. Therefore, a command to maintain the current mode is generated.

[0026] After completing all the above logical combination judgments, the buck mode instruction, boost mode instruction, or maintain current mode instruction generated by the judgment will be output as the target operating mode instruction.

[0027] The target operating mode command is directly used to control the on / off combination of each branch switch in the bypass switching switch and the duty cycle adjustment direction of the bidirectional switching transistor inside the AC / AC converter, thereby driving the distribution network into the corresponding voltage regulation operating mode.

[0028] The method was deployed in a low-voltage distribution transformer area that was actually in operation. The area was powered by a 630 kVA 10 kV / 380 V distribution transformer with a power supply radius of about 600 meters. It was connected to 180 kW of distributed photovoltaic power, 15 DC charging piles, and more than 200 residential users. The intelligent integrated terminal of the transformer area was installed in the main switch cabinet on the low-voltage side of the transformer.

[0029] The terminal synchronously collects the A-phase voltage at the transformer outlet and the load side at the end of the distribution area at 256 sampling points per power frequency cycle. The preset upper limit of the voltage is 235.4 volts and the lower limit is 198 volts, and the data is stored in the terminal's comparison register.

[0030] At 12:30 PM, the photovoltaic output reached 160 kW, while residential electricity consumption was only 30 kW. Due to power backfeeding, the terminal voltage rose to 244.2 volts, exceeding the upper limit of 235.4 volts. The comparator output an upper limit indicator, and the current operating mode was bypass direct mode. The logic determined and generated a step-down mode command. The bypass switching switch connected the AC / AC converter in series, and the duty cycle was adjusted to reduce the load-side voltage from 244.2 volts to 226 volts, entering the qualified range of 198 volts to 235.4 volts. The entire adjustment was completed within 20 power frequency cycles, and the terminal continuously monitored and did not trigger the upper limit again.

[0031] At 8:30 p.m. that evening, residential electricity consumption reached 170 kilowatts, photovoltaic output was zero, and the transformer output voltage dropped to 192.6 volts, below the lower limit of 198 volts. The comparator output exceeded the lower limit indicator, indicating that the current mode was step-down. The logic determined and generated a step-up mode instruction, and the bypass switch was switched to step-up access mode. The duty cycle was adjusted to increase the load-side voltage from 192.6 volts to 208 volts, returning it to the qualified range.

[0032] Under both typical operating conditions, this method accurately outputs boost / buck commands based on the real-time combination of the voltage over-limit indicator and the current mode indicator, avoiding the false issuance of repeated commands in the same direction and the false switching of the regulation mode when the voltage is normal.

[0033] After this method was deployed in the area, it operated continuously for three months. A total of 68 instances of voltage exceeding the upper limit and 52 instances of voltage exceeding the lower limit occurred. Each time, the target mode command was correctly generated. After voltage regulation, the load-side voltage stabilized within the range of 198 volts to 235.4 volts, and no command misjudgment or switching oscillation occurred.

[0034] Actual operation records show that the instructions generated by this method are accurate and reliable, meet the real-time control requirements of the bidirectional voltage regulation device, effectively improve the voltage quality of the distribution area, and ensure full grid connection of distributed photovoltaic power and normal electricity use for residents.

[0035] Step 2: In the distribution network, the direction and amplitude of the inductor current and the phase difference between the port voltages of the grid side and the load side are fused and sorted to construct a switching window prediction sequence and determine the optimal switching time window; In this embodiment of the invention, the process of fusing and sorting the direction and amplitude of the inductor current and the phase difference between the port voltages of the grid side and the load side in the distribution network, constructing a switching window prediction sequence, and determining the optimal switching time window is as follows: The instantaneous values ​​of the inductor current at multiple consecutive sampling times are obtained, the direction of the inductor current is determined according to the positive and negative polarities of the instantaneous values, and the absolute value of the instantaneous values ​​is taken as the amplitude of the inductor current. Calculate the time difference between the port voltages of the grid side and the load side in the distribution network at the zero crossing moment, and take the ratio between the time difference and the power frequency period of the distribution network as the phase difference between the port voltages of the grid side and the load side. The current inductor current direction, current amplitude, and port voltage phase difference are weighted and fused according to preset weighting coefficients to obtain the switching window evaluation value of the distribution network at the current moment. Based on the current time, slide forward a preset time window length, calculate the switching window evaluation value corresponding to each time within the preset time window length in turn, and sort each time according to the switching window evaluation value from best to worst to obtain the switching window prediction sequence. The optimal switching time window is obtained by selecting the time with the best evaluation value from the switching window prediction sequence as the center time and expanding outward with a preset width centered on the center time.

[0036] Continuous sampling is performed on the inductor branches in the distribution network to obtain the instantaneous current values ​​corresponding to multiple sampling times. These instantaneous current values ​​are arranged into a sequence of instantaneous inductor current values ​​according to the chronological order of the sampling times. The sampling operation is performed by the analog-to-digital conversion module inside the intelligent converged terminal of the distribution area. This module collects the output signal of the secondary side of the current transformer on the inductor branch at a fixed sampling frequency. Each sampling time corresponds to a sampling pulse. When the sampling pulse arrives, the analog-to-digital conversion module converts the analog current signal at the current moment into a digital quantity, which is the instantaneous current value at that moment. The sign of each instantaneous current value is read from the sequence of instantaneous inductor current values. When the instantaneous current value is positive, the direction of the inductor current is determined to be positive; when the instantaneous current value is negative, the direction of the inductor current is determined to be negative. A positive sign indicates that the inductor current flows from the grid side to the load side, and a negative sign indicates that the inductor current flows from the load side to the grid side, thus obtaining the direction of the inductor current. Take the absolute value of each instantaneous current value. This absolute value is the inductor current amplitude corresponding to that sampling moment. This gives the inductor current amplitude corresponding to each sampling moment.

[0037] Zero-crossing detection is performed on the continuous time-domain waveform of the grid-side port voltage in the distribution network. This zero-crossing detection is completed by a voltage comparator circuit inside the terminal. The comparator compares the grid-side port voltage signal with a zero-volt reference voltage in real time. When the grid-side port voltage signal rises from a negative value, crosses zero volts, and enters the positive voltage range, the comparator outputs a rising edge pulse signal. The moment this rising edge pulse signal appears is the moment when the grid-side port voltage waveform changes from negative to positive and crosses the zero-volt level. This moment is recorded as the grid-side zero-crossing moment. Zero-crossing detection is also performed on the continuous time-domain waveform of the load-side port voltage in the distribution network. This zero-crossing detection is completed by another set of voltage comparator circuits inside the terminal. The comparator compares the load-side port voltage signal with a zero-volt reference voltage in real time. When the load-side port voltage signal rises from a negative value, crosses zero volts, and enters the positive voltage range, the comparator outputs a rising edge pulse signal. The moment this rising edge pulse signal appears is the moment when the load-side port voltage waveform changes from negative to positive and crosses the zero-volt level. This moment is recorded as the load-side zero-crossing moment. Calculate the absolute value of the difference between the zero-crossing time on the grid side and the zero-crossing time on the load side. The absolute value of this difference is calculated by subtracting the time value corresponding to the zero-crossing time on the load side from the time value corresponding to the zero-crossing time on the grid side. If the result is negative, take its opposite. The final time length is the phase difference between the port voltages on the grid side and the load side at the zero-crossing time.

[0038] The power frequency cycle duration of the distribution network is obtained. This power frequency cycle duration is the fixed time required for the AC voltage of the distribution network to complete a full sine wave. For my country's low-voltage distribution network, this duration is 0.02 seconds. The time difference between the zero-crossing moments of the grid-side and load-side port voltages is divided by the power frequency cycle duration of the distribution network. The resulting ratio is the phase difference between the grid-side and load-side port voltages, representing the relative offset of the grid-side and load-side voltages on the time axis. A first preset weighting coefficient is assigned to the inductor current direction, a second preset weighting coefficient is assigned to the inductor current amplitude, and a third preset weighting coefficient is assigned to the port voltage phase difference. All three weighting coefficients are positive numbers between zero and one, and their sum equals one. The relative magnitudes of the three weighting coefficients are predetermined based on physical principles. The magnitude of the inductor current amplitude directly determines the current value disconnected during switch switching and has the greatest impact on switching impact; therefore, the second preset weighting coefficient is the maximum value among the three.

[0039] The phase difference of the port voltage determines the synchronization degree between the grid-side voltage and the load-side voltage, and its impact on switching impact is secondary; therefore, the third preset weighting coefficient is taken as the middle value. The direction of the inductor current only determines the current flow direction and has the least impact on switching impact; therefore, the first preset weighting coefficient is taken as the minimum value among the three. The current inductor current direction is expressed numerically: when the inductor current direction is positive, the value is taken as positive one; when the inductor current direction is negative, the value is taken as negative one. This value is multiplied by the first preset weighting coefficient to obtain the direction-weighted value. The current inductor current amplitude is divided by the distribution network rated current value, which is pre-stored in the terminal's non-volatile memory. The quotient of this division is the normalized amplitude. The physical meaning of the normalized amplitude is to unify the amplitudes under different current levels to the same dimension range so that it can be weighted and summed with the direction value and phase difference. The normalized amplitude is multiplied by the second preset weighting coefficient to obtain the amplitude-weighted value.

[0040] The current phase difference of the port voltage is divided by the maximum phase difference corresponding to the power frequency cycle, which is one. The quotient of this division is the normalized phase difference. The physical meaning of the normalized phase difference is to convert the phase difference from a time dimension to a dimensionless ratio so that it can be summed with other weighting terms. The normalized phase difference is multiplied by the third preset weighting coefficient to obtain the phase difference weighted value. The direction weighted value, amplitude weighted value, and phase difference weighted value are summed to obtain the switching window evaluation value of the distribution network at the current moment. The larger the switching window evaluation value, the closer the instantaneous value of the inductor current is to zero when the bypass switching switch is turned on and off at that moment. The smaller the phase difference between the grid-side voltage and the load-side voltage, the less severe the voltage spikes and current impacts generated by the switching process on the distribution network, and the smoother the switching transition process.

[0041] Using the current time as the reference time, a preset time window length is traced back from the corresponding time value. The preset time window length is a fixed value set according to the power frequency cycle of the distribution network, typically three or five power frequency cycles. The starting time for tracing back is obtained by subtracting the preset time window length from the reference time. The continuous time range between the starting time for tracing back and the current time is the time window to be analyzed. Within this time window, multiple historical times are selected sequentially at fixed time intervals. The fixed time interval is the sampling period of the terminal analog-to-digital conversion module, and the time difference between two adjacent sampling times is always equal to the sampling period. For each selected historical time, the inductor current direction, inductor current amplitude, and port voltage phase difference corresponding to that historical time are read according to the aforementioned calculation methods of direction weighting, amplitude weighting, and phase difference weighting. These values ​​are then multiplied by their respective preset weighting coefficients and summed to obtain the switching window evaluation value corresponding to that historical time. The above calculation process is repeated until all selected historical times within the time window have obtained their corresponding switching window evaluation values, thus obtaining the switching window evaluation values ​​corresponding to each time within the preset time window length.

[0042] All moments within a preset time window are arranged in descending order of their respective switching window evaluation values, with the moment with the highest evaluation value placed first, the second highest second, and the lowest last. This forms a sequence of moments arranged from best to worst, which is the switching window prediction sequence. Moments earlier in the sequence correspond to smaller inductor current amplitudes and smaller phase differences, posing a lower risk of impact when switching is performed at these moments. Conversely, moments later in the sequence correspond to larger inductor current amplitudes and larger phase differences, posing a higher risk of impact when switching is performed at these moments. The moment with the highest switching window evaluation value, placed first in the sequence, is selected as the center moment. This moment represents the moment within the preset time window where the inductor current amplitude is closest to zero, the phase difference is smallest, and the overall switching conditions are optimal.

[0043] Using the center time as the center of symmetry, the time length corresponding to the preset width is extended forward on the time axis. The preset width is a pre-fixed time length value, which is less than the preset time window length and is usually half a power frequency cycle or a quarter of a power frequency cycle. The forward extension method is to subtract the time length corresponding to the preset width from the time value corresponding to the center time. The resulting time is the window start boundary time.

[0044] Using the center time as the center of symmetry, the time axis is extended backward by a preset width corresponding to a certain time length. This extension is achieved by adding the preset width to the time value corresponding to the center time. The resulting time is the window's termination boundary time. The continuous time interval between the window's start and end boundary times constitutes the optimal switching time window. The center time of this optimal switching time window represents the time with the best switching conditions. The switching conditions in the region near the center time within the window are also excellent, while the switching conditions at the window boundaries are slightly worse but still better than most times within the preset time window length.

[0045] The optimal switching time window is used to limit the time range in which each branch switch of the bypass switching switch actually performs on / off switching operations. Any time within this range is suitable for switching. Limiting the switching operation to this window can minimize voltage spikes and current surges.

[0046] This method was applied to a bidirectional voltage regulation device in a low-voltage distribution substation. The substation is powered by a 630 kVA 10 kV / 380 V distribution transformer. The inductor branch is a series-connected filter inductor with an inductance value of 0.5 millihenries and a power frequency cycle of 0.02 seconds. The terminal synchronously samples the inductor current, grid-side voltage, and load-side voltage at 128 sampling points per power frequency cycle.

[0047] The preset time window length is 0.06 seconds, the preset width is 0.01 seconds, and the weighting coefficients for the inductor current direction, amplitude, and port voltage phase difference are set to 0.2, 0.5, and 0.3, respectively.

[0048] At a certain moment, the terminal collected an instantaneous value of -35 Amperes for the inductor current, determined the direction to be negative, and the amplitude to be 35 Amperes. At the same time, it detected that the time difference between the zero crossing of the voltage at the grid side and the load side was 0.002 seconds, which, when divided by the power frequency period, yielded a phase difference of 0.1.

[0049] The negative value of direction (-1) multiplied by the weight (0.2) yields the weighted value of direction (-0.2). The amplitude (35) divided by the rated current (200) yields the normalized amplitude (0.175), which is multiplied by the weight (0.5) to obtain the weighted amplitude value (0.0875). The phase difference (0.1) divided by the maximum value (1) yields the normalized phase difference (0.1), which is multiplied by the weight (0.3) to obtain the weighted phase difference value (0.03). The sum of these three values ​​yields the current switching window evaluation value (-0.0825).

[0050] The terminal backtracks 0.06 seconds from the current time and selects 384 historical times at sampling intervals, calculating their respective evaluation values. The maximum value of 0.035 corresponds to a time 0.023 seconds before the current time. This time is determined as the center time and extended forward and backward by 0.005 seconds to obtain an optimal switching time window with a width of 0.01 seconds, which highly coincides with the natural zero-crossing interval of the inductor current.

[0051] The terminal sends a switch on / off control signal within the window. The measured inductor current at the moment of switching is only 2 amps, which is much less than the peak value of 35 amps. There are no voltage spikes, no current surges, and no arcing at the switch contacts.

[0052] If this method is not used and the switch is directly switched at the 35 Ampere peak time, the measured overvoltage reaches 1.8 times the rated voltage and the overcurrent reaches 2.3 times the rated current, and the switch contacts are obviously arcing and burning.

[0053] Based on 30 consecutive switching operation records, this method was used to determine that the switching was performed within the window. The instantaneous inductor current was less than or equal to 3 amps each time, with no arcing, no overshoot, no voltage spikes, and no abnormal burning or wear of the contacts.

[0054] Step 3: Within the optimal switching time window, according to the target operation mode instruction, arrange the pre-conduction states of the bypass switching switches in the distribution network into a switch pre-action timing matrix; In this embodiment of the invention, the process of arranging the pre-conduction states of the bypass switching switches in the distribution network into a switch pre-action timing matrix according to the target operation mode instruction within the optimal switching time window is as follows: Read the current on / off status of each branch switch in the bypass switching switch in the distribution network; Query the pre-conduction target state of each branch switch corresponding to the target operation mode command from the preset switch state mapping table; Compare the current on / off state of each branch switch with the target state of pre-conduction to determine the target branch switch whose state needs to be changed and the corresponding target state. According to the preset switching sequence within the optimal switching time window, the target branch switches and their corresponding target states are arranged in the order of action to generate a switching action sequence. The switching action sequence is encoded into a binary matrix with each branch switch as the row and the time tick as the column, thus obtaining the switch pre-action timing matrix.

[0055] The on / off status of each branch switch in the bypass switching switch in the distribution network is read. This reading operation is performed by the intelligent fusion terminal of the distribution area sending a status query signal to the auxiliary contact or status register of each branch switch through its general input / output interface. After receiving the query signal, each branch switch returns its actual on / off status signal at the current moment. When the signal is high, it indicates that the branch switch is in the conducting state, and when it is low, it indicates that the branch switch is in the off state.

[0056] The terminal records the high or low level signal returned by each branch switch as the current on / off state of that branch switch. The current on / off states of all branch switches together constitute the current on / off state set of the bypass switching switch.

[0057] The terminal internally stores a switch state mapping table, which records the correspondence between each possible value of the target operating mode command and the pre-conduction target state that each branch switch should be in, in tabular form. When the terminal receives the target operating mode command, it uses the specific content of the target operating mode command as an index to search for the corresponding row in the switch state mapping table. From that row, it sequentially reads the pre-conduction target state corresponding to each branch switch, which includes both on and off states. After reading all the states, it obtains the set of pre-conduction target states that each branch switch should be in when matching the target operating mode command.

[0058] The terminal compares the current on / off state of each branch switch with its pre-conduction target state, one by one, according to the switch name. For each branch switch, it compares whether its current on / off state and pre-conduction target state are consistent. If the current on / off state of a branch switch is the same as its pre-conduction target state, it is determined that the branch switch does not need to change its state. If the current on / off state of a branch switch is different from its pre-conduction target state, it is determined that the branch switch needs to change its state, and the branch switch is identified as the target branch switch. At the same time, the pre-conduction target state of the branch switch is determined as its corresponding target state.

[0059] After comparing each branch switch item by item, all branch switches determined to need a state change and their corresponding target states are summarized to obtain a complete list of target branch switches requiring a state change and their corresponding target states. The terminal obtains the start and end times of the optimal switching time window and reads the pre-set switching sequence within that window from the timing generator inside the terminal. This switching sequence defines multiple time beats arranged sequentially within the optimal switching time window, with each time beat corresponding to a fixed time point, and the time interval between each time beat equal to the minimum time resolution of the terminal drive pulse.

[0060] The terminal assigns the target branch switches whose states need to be changed to various time cycles in the switching sequence, ensuring that each target branch switch is assigned to a specific time cycle. During the assignment process, if the physical actions of multiple target branch switches do not affect each other and simultaneous action will not cause electrical conflict, these target branch switches are assigned to the same time cycle. If the simultaneous action of two target branch switches would cause a dangerous state such as a short circuit or open circuit inside the bypass switch, these two target branch switches are assigned to different time cycles, causing them to act sequentially at different times.

[0061] After all allocations are completed, the terminal arranges each time clock, its assigned target switch, and its corresponding target state in sequential order, forming a complete action sequence from the first time clock to the last time clock. This action sequence is the switch action sequence. Each item in this switch action sequence contains three information elements: the time clock in which the action is performed, the name of the target switch to be performed, and the target state that the target switch needs to achieve.

[0062] The terminal constructs a blank binary matrix. The number of rows in this matrix is ​​equal to the total number of branch switches in the bypass switching system, and the number of columns is equal to the total number of preset time ticks within the optimal switching window. The terminal pre-assigns a fixed branch switch to each row and a fixed time tick to each column. The intersection of the row and column represents the state value of that branch switch at that time tick. The terminal sequentially reads each target branch switch, its assigned time tick, and the corresponding target state from the switch action sequence, locating the row and column corresponding to that target branch switch in the matrix. If the target state of the target branch switch is "on," the terminal enters the value 1 at the intersection of the row and column. If the target state of the target branch switch is "off," the terminal enters the value 0 at the intersection of the row and column. For the intersection of a branch switch and a time cycle not involved in the switching action sequence, the terminal fills in the value corresponding to the current on / off state of the branch switch. If the current on / off state is on, fill in 1; if the current on / off state is off, fill in 0.

[0063] Repeat the above filling operation until all the intersections of all rows and columns in the matrix are filled with the value 1 or 0. The final complete binary matrix is ​​the switch pre-action timing matrix. Each row in this switch pre-action timing matrix completely records the state change trajectory of the corresponding branch switch over all time cycles, and each column completely records the state distribution of all branch switches over the same time cycle.

[0064] This step was applied to a bidirectional voltage regulation device in a low-voltage distribution area. The area is powered by a 630 kVA 10 kV / 380 V distribution transformer. The bypass switching device includes six branch switches: a first grid-side switch, a first load-side switch, a second grid-side switch, a second load-side switch, a bypass main switch, and a redundant protection switch.

[0065] The terminal generates a step-down mode command as the target operating mode command and reads the current on / off status of the six switches as follows: the first grid-side switch is on, the first load-side switch is on, the second grid-side switch is off, the second load-side switch is off, the bypass main switch is off, and the redundant protection switch is on.

[0066] The pre-conduction target states corresponding to the buck mode in the terminal internal switch state mapping table are: first grid-side switch off, first load-side switch off, second grid-side switch on, second load-side switch on, bypass main switch off, and redundant protection switch off.

[0067] After comparing each item, the terminal determined that the five target branch switches that need to change their status are: the first grid-side switch is off, the first load-side switch is off, the second grid-side switch is on, the second load-side switch is on, the redundant protection switch is off, and the bypass main switch remains off and does not operate.

[0068] The optimal switching time window is from 0.008 seconds to 0.018 seconds after the current time. Ten time cycles are preset within the window, with an interval of 0.001 seconds between each cycle. The terminal is allocated according to the switching sequence: in the first cycle, the redundant protection switch is turned off; in the second cycle, the first grid-side switch and the first load-side switch are turned off simultaneously; in the third cycle, the second grid-side switch and the second load-side switch are turned on simultaneously; and there is no action from the fourth to the tenth cycle, thus generating a switching action sequence.

[0069] The terminal constructs a six-row, ten-column binary matrix. The six rows correspond to six switches, and the ten columns correspond to the first to tenth phases. Values ​​are filled into each column. In the first phase, the row containing the redundant protection switch is filled with 0, and the remaining rows are filled with the current state value. In the second phase, the row containing the first grid-side switch and the first load-side switch is filled with 0, and the remaining rows are filled with the current state value. In the third phase, the row containing the second grid-side switch and the second load-side switch is filled with 1, and the remaining rows are filled with the current state value. In the fourth to tenth phases, the final state value after the switching is completed is filled in, resulting in a complete switch pre-action timing matrix.

[0070] Within the optimal switching window, the terminal outputs drive signals column by column in a matrix. The five target branch switches complete the switching in an orderly manner within three cycles. No short circuit caused by simultaneous conduction or open circuit caused by simultaneous deactivation occurs during the switching process.

[0071] This step, used in conjunction with the optimal switching time window determination step, ensured that the matrix was correctly generated and the bypass switching switch was smoothly driven to switch smoothly in multiple buck-boost switching operations over three consecutive months in this distribution area, without any electrical accidents caused by incorrect switching sequence.

[0072] Step 4: Calculate the pre-switching duty cycle reference value based on the voltage regulation ratio corresponding to the target operating mode command, and adjust the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value. In this embodiment of the invention, the process of calculating the pre-switching duty cycle reference value based on the voltage regulation ratio corresponding to the target operating mode command, and adjusting the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value, is as follows: Decode the target operating mode command to identify the voltage regulation direction and voltage regulation amplitude corresponding to the target operating mode command. The voltage regulation direction includes either the voltage boosting direction or the voltage bucking direction, and the voltage regulation amplitude includes the voltage regulation ratio value corresponding to the target operating mode command. Calculate the pre-switching duty cycle reference value based on the voltage regulation direction and voltage regulation amplitude; The difference between the current duty cycle of the bidirectional switching transistor inside the AC / AC converter and the reference value of the pre-switching duty cycle is used as the duty cycle adjustment deviation. Based on the positive and negative directions of the duty cycle adjustment deviation, the duty cycle adjustment direction of the bidirectional switch is determined, and the duty cycle of the bidirectional switch is gradually changed according to the preset single adjustment step size until the duty cycle of the bidirectional switch reaches the pre-switching duty cycle reference value.

[0073] The process of calculating the pre-switching duty cycle reference value based on the voltage regulation direction and voltage regulation amplitude is as follows: Obtain the high-voltage side port voltage sampling value and the low-voltage side port voltage sampling value inside the AC / AC converter; Based on the voltage regulation direction, one of the voltage sampling values ​​at the high-voltage side port and the low-voltage side port is determined as the reference voltage, and the other is determined as the target voltage. When the voltage regulation direction is the boost direction, the high voltage side port voltage sampling value is used as the reference voltage and the low voltage side port voltage sampling value is used as the target voltage. When the voltage regulation direction is the voltage reduction direction, the low-voltage side port voltage sampling value is used as the reference voltage and the high-voltage side port voltage sampling value is used as the target voltage. The ratio of the target voltage to the reference voltage is used as the voltage transfer ratio, and divided by the equivalent gain coefficient of the AC / AC converter in the current operating state, to obtain the pre-switching duty cycle reference value.

[0074] The target operating mode instruction inside the terminal is stored in the instruction register in the form of a multi-bit binary code. Different segments of this code carry voltage regulation direction information and voltage regulation amplitude information, respectively.

[0075] The terminal reads the complete binary code of the target operating mode instruction from the instruction register, extracts the bit segment value specifically used to indicate the voltage regulation direction, and identifies a voltage boost direction when the bit segment value is 1, and a voltage buck direction when the bit segment value is 0, thus obtaining the voltage regulation direction. The terminal also extracts the bit segment value specifically used to indicate the voltage regulation amplitude from the binary code of the target operating mode instruction. This bit segment value directly corresponds to a voltage regulation ratio value, which represents the adjustment range of the load-side voltage relative to the grid-side voltage required by the target operating mode instruction. The terminal reads this bit segment value and converts it into a voltage regulation ratio value, thus obtaining the voltage regulation amplitude.

[0076] After the terminal completes the full decoding of the target operating mode command, it simultaneously obtains two pieces of information: the voltage regulation direction and the voltage regulation amplitude. The voltage regulation direction is either the voltage boosting direction or the voltage bucking direction, and the voltage regulation amplitude is a specific voltage regulation ratio value.

[0077] The terminal's internal analog-to-digital conversion module samples the voltage signals at the high-voltage side and low-voltage side ports of the AC / AC converter, obtaining the high-voltage side port voltage sample value and the low-voltage side port voltage sample value, both of which are instantaneous values ​​of the port voltage at the current moment. The terminal determines the reference voltage and target voltage based on the decoded voltage regulation direction. When the voltage regulation direction is boost, the terminal determines the high-voltage side port voltage sample value as the reference voltage and the low-voltage side port voltage sample value as the target voltage. When the voltage regulation direction is buck, the terminal determines the low-voltage side port voltage sample value as the reference voltage and the high-voltage side port voltage sample value as the target voltage. After determining the reference voltage and target voltage, the terminal divides the target voltage value by the reference voltage value; the resulting ratio is the voltage transfer ratio. This voltage transfer ratio indicates the required ratio between the output voltage and input voltage for the AC / AC converter during actual operation.

[0078] The terminal internally stores the equivalent gain coefficient of the AC / AC converter in the current operating state. This equivalent gain coefficient is determined by the AC / AC converter topology and is fixedly stored in the terminal's non-volatile memory after factory calibration. It represents the voltage transfer ratio that the converter can achieve when the duty cycle of the bidirectional switch is at its maximum. The terminal divides the voltage transfer ratio by the equivalent gain coefficient, and the quotient is the pre-switching duty cycle reference value. This reference value represents the target duty cycle value that the bidirectional switch needs to achieve under the voltage regulation direction and voltage regulation amplitude required by the target operating mode command.

[0079] The terminal reads the actual pulse width modulation (PWM) signal duty cycle of the bidirectional switching transistor inside the AC / AC converter at the current moment through the driver circuit interface; this value is the current duty cycle. The terminal subtracts the pre-switching duty cycle reference value from the current duty cycle value; the difference is the duty cycle adjustment deviation. When the current duty cycle is greater than the pre-switching duty cycle reference value, the duty cycle adjustment deviation is positive, indicating that the duty cycle needs to be decreased. When the current duty cycle is less than the pre-switching duty cycle reference value, the duty cycle adjustment deviation is negative, indicating that the duty cycle needs to be increased.

[0080] The terminal determines the duty cycle adjustment direction of the bidirectional switch based on the sign of the duty cycle adjustment deviation. If the deviation is positive, the adjustment direction is decreasing; if the deviation is negative, the adjustment direction is increasing. The terminal has a preset single adjustment step size, which is a fixed duty cycle change value. Each adjustment operation can only change the size of one step. Starting with the current duty cycle, the terminal increases or decreases the current duty cycle by one single adjustment step size in each switching cycle according to the determined duty cycle adjustment direction, obtaining an updated duty cycle value. The terminal compares the updated duty cycle value again with the pre-switching duty cycle reference value and recalculates the duty cycle adjustment deviation. If the absolute value of the new duty cycle adjustment deviation is still greater than zero, the terminal again increases or decreases the duty cycle by one single adjustment step size in the same direction in the next switching cycle.

[0081] The terminal repeatedly performs the above comparison and single-step adjustment operations. After each adjustment, the updated duty cycle is output to the pulse width modulation signal generation circuit of the bidirectional switch until the current duty cycle value is equal to the pre-switching duty cycle reference value. At this time, the duty cycle adjustment deviation is zero, the terminal stops the adjustment operation, and the duty cycle of the bidirectional switch stabilizes at the pre-switching duty cycle reference value.

[0082] The method for calculating and adjusting the pre-switching duty cycle reference value was applied to a bidirectional voltage regulation device in a low-voltage distribution area. The area is powered by a 630 kVA 10 kV / 380 V distribution transformer. The AC / AC converter is connected to the grid bus on the high-voltage side and the load line on the low-voltage side.

[0083] At a certain moment, the terminal generates a boost mode command. After decoding, the voltage regulation direction is determined to be the boost direction, and the voltage regulation ratio is 1.1. The high-voltage side voltage is sampled as 220 volts and the low-voltage side voltage as 200 volts. Since the boost direction is determined, the high-voltage side 220 volts is determined as the reference voltage and the low-voltage side 200 volts is determined as the target voltage. The target voltage is divided by the reference voltage to obtain the voltage transfer ratio of 0.909. The equivalent gain coefficient of 0.95 is read from the memory. The voltage transfer ratio is divided by the gain coefficient to obtain the pre-switching duty cycle reference value of 0.957.

[0084] The terminal reads the current duty cycle as 0.5, subtracts the reference value of 0.957 to get a deviation of -0.457. The negative value indicates that the duty cycle needs to be increased. The preset single adjustment step size is 0.001, and it increases by 0.001 in each switching cycle. After 457 cycles, the duty cycle gradually increases from 0.5 to 0.957, taking about 0.023 seconds. The converter output voltage smoothly rises from 200 volts to 220 volts without sudden changes or overshoot.

[0085] In another operation, the terminal generated a step-down mode command with the voltage adjustment direction being the step-down direction, a ratio of 0.9, sampling 235V on the high-voltage side and 230V on the low-voltage side. Due to the step-down direction, the low-voltage side 230V was determined as the reference voltage and the high-voltage side 235V as the target voltage. The voltage transfer ratio was 1.022, which, divided by the gain coefficient of 0.95, yielded a reference value of 1.076. The voltage was limited to the maximum value of 1, with a current duty cycle of 0.8 and a deviation of -0.2. The deviation was gradually increased to 1 in steps of 0.001, completing the process in 200 cycles. The output voltage dropped from 230V to 218V, achieving the step-down target.

[0086] Actual operation shows that this method obtains the pre-switching duty cycle reference value by decoding the command, determining the reference and target voltages, calculating the voltage transfer ratio and dividing it by the equivalent gain coefficient, and then adjusting it step by step. The buck-boost adjustment is without impact or oscillation, and the load-side voltage is stable within the qualified range.

[0087] Step 5: When the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window, according to the switch pre-action timing matrix, the on / off switching of each branch switch in the bypass switching switch is performed, and after the switching is completed, the duty cycle of the bidirectional switching tube is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to the preset slope, so as to obtain the voltage regulation operation state after the disturbanceless switching. In this embodiment of the invention, when the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window, the on / off switching of each branch switch in the bypass switching switch is performed according to the switch pre-action timing matrix. After the switching is completed, the duty cycle of the bidirectional switching transistor is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to a preset slope, so as to obtain the voltage regulation operation state after the disturbance-free switching. The process is as follows: The instantaneous value of the inductor current in the distribution network is compared with the preset zero current threshold. When the instantaneous value of the inductor current is less than or equal to the preset zero current threshold, it is determined that the inductor current has entered the zero current state, and the duration of the inductor current in the zero current state is recorded. When the duration is greater than or equal to the preset duration threshold, the inductor current is determined to be in the zero current crossover interval corresponding to the optimal switching time window. Within the zero current crossing range, the action sequence of each branch switch in the pre-action timing matrix of the switch is analyzed, and the on / off control signal of each branch switch is output sequentially according to the action order in the action sequence of each branch switch, so as to complete the on / off switching of all branch switches to be operated in the bypass switching switch. After detecting that all the switch to be operated has completed the on / off switching, the difference between the target steady-state duty cycle corresponding to the target operating mode command and the pre-switching duty cycle reference value is divided by the preset number of adjustment steps to obtain the single-step adjustment amount. According to the preset slope, the duty cycle of the bidirectional switching transistor is increased by a single-step adjustment amount in every two adjacent switching cycles until the duty cycle of the bidirectional switching transistor reaches the target steady-state duty cycle, thus obtaining the voltage regulation operation state after disturbance-free switching.

[0088] The current sampling module inside the terminal continuously samples the output signal of the secondary side of the current transformer on the inductor branch in real time to obtain the instantaneous current value of the inductor current at the current sampling moment.

[0089] The terminal internally stores a preset zero-current threshold, a positive value close to zero amperes, used to determine whether the inductor current has decreased to a level where its impact on switching surges can be ignored. At each sampling moment, the terminal compares the sampled instantaneous inductor current value with the preset zero-current threshold. If the instantaneous value is less than or equal to the preset zero-current threshold, the inductor current is determined to have entered a zero-current state at that sampling moment. When the inductor current is determined to have entered a zero-current state, an internal timer starts counting, recording the length of time the inductor current remains in the zero-current state; this length is the duration. The terminal continuously monitors the instantaneous inductor current value in each sampling cycle. If the instantaneous value at a certain sampling moment is greater than the preset zero-current threshold, the inductor current is determined to have exited the zero-current state, the timer immediately resets to zero and stops counting.

[0090] The terminal compares the duration recorded by the timer with a preset duration threshold stored internally. The preset duration threshold is set to a length of time that ensures the inductor current truly and stably crosses zero, rather than experiencing instantaneous disturbances. When the duration is greater than or equal to the preset duration threshold, the terminal determines that the inductor current is currently within the zero-current crossing interval corresponding to the optimal switching time window. Within this interval, the inductor current maintains a near-zero value for a sufficient period of time, meeting the safety conditions for performing the bypass switching switch on / off switching. After confirming that the inductor current is within the zero-current crossing interval, the terminal reads the previously generated switch pre-action timing matrix. This switch pre-action timing matrix consists of multiple rows and multiple columns. Each row corresponds to a branch switch, and each column corresponds to a time cycle. The value 1 or 0 at each position in the matrix indicates that the branch switch should be in the on or off state at that time cycle.

[0091] The terminal parses the matrix column by column, starting from the first column. For each column, it reads the values ​​corresponding to all rows in that column to obtain the target on / off state of each branch switch in that time cycle. The terminal compares the target on / off state of each branch switch in the current time cycle with the actual on / off state of each branch switch before that time cycle, and marks those branch switches whose target state is inconsistent with their actual state. These branch switches are the branch switches that need to be activated in that time cycle.

[0092] For each marked branch switch to be activated, the terminal generates an on / off control signal. A high level signal turns the branch switch on, and a low level signal turns it off. The specific signal level is determined based on the target on / off state of the branch switch in that time cycle. The terminal outputs all generated on / off control signals sequentially to the corresponding branch switch's drive circuit in the bypass switching mechanism, according to the time cycle sequence. Upon receiving the signal, the drive circuit performs the corresponding on or off operation. After completing the output of all control signals for one time cycle, the terminal waits for the next time cycle, then continues to analyze the next column of the matrix, generating and outputting the next set of control signals.

[0093] The terminal repeats the process of parsing and outputting control signals column by column until all columns in the switch pre-action timing matrix have been processed. At this point, all branch switches requiring state changes have completed their on / off switching according to the predetermined timing. During the on / off switching process of each branch switch in the bypass switching switch, the terminal continuously monitors the drive circuit feedback signal of each branch switch to be activated. This feedback signal indicates that the branch switch has actually reached the target on or off state. Each time the terminal detects a feedback signal from a branch switch and confirms that it has completed the switching, it marks that branch switch as having completed the switching.

[0094] When the terminal detects that the feedback signals of all pending branch switches have been marked as completed, the terminal determines that all on / off switching operations of the bypass switching switch have been completed, and generates a switching completion confirmation signal. After receiving the switching completion confirmation signal, the terminal reads the target steady-state duty cycle corresponding to the target operating mode command. This target steady-state duty cycle is a final duty cycle value calculated in advance based on voltage regulation requirements and converter characteristics, used to maintain the output voltage stable within the qualified range after switching. The terminal simultaneously reads the current actual duty cycle value of the bidirectional switching transistor, which is the pre-switching duty cycle reference value used during the switching execution. The terminal subtracts the pre-switching duty cycle reference value from the target steady-state duty cycle value to obtain the difference between the two. This difference represents the total magnitude of the duty cycle change required from the pre-switching reference value to the target steady-state value. The terminal internally stores a preset number of adjustment steps, which is a fixed positive integer representing the total number of steps required to adjust from the pre-switching duty cycle reference value to the target steady-state duty cycle. The terminal divides the difference between the target steady-state duty cycle and the pre-switching duty cycle reference value by the preset number of adjustment steps. The quotient obtained is the amount by which the duty cycle needs to be changed in each adjustment step. This quotient is defined as the single-step adjustment amount. A positive single-step adjustment amount indicates that the duty cycle needs to be gradually increased, and a negative single-step adjustment amount indicates that the duty cycle needs to be gradually decreased.

[0095] Starting from the current moment, the terminal divides the subsequent time into clock cycles according to the switching period of the bidirectional switch, with each switching cycle constituting an adjustment time unit. The terminal combines two adjacent switching cycles into an adjustment group. During the first switching cycle of each adjustment group, the current duty cycle of the bidirectional switch remains unchanged. During the second switching cycle of the same adjustment group, the current duty cycle is increased by a single-step adjustment amount. At the end of the second switching cycle of each adjustment group, the terminal outputs the updated duty cycle value to the pulse width modulation signal generation circuit of the bidirectional switch, driving the bidirectional switch to conduct according to the new duty cycle. After each adjustment group ends, the terminal compares the current duty cycle value with the target steady-state duty cycle value. If the current duty cycle has not yet reached the target steady-state duty cycle, the next adjustment group is executed. During the first switching cycle of the next adjustment group, the current duty cycle remains unchanged, and during the second switching cycle, another single-step adjustment amount is added.

[0096] The terminal repeats the above operation of stepping every two switching cycles until the absolute difference between the current duty cycle and the target steady-state duty cycle is less than the value of the single-step adjustment. At this point, the terminal directly sets the current duty cycle to the target steady-state duty cycle value and stops stepping adjustment. At this time, the duty cycle of the bidirectional switch is stable at the target steady-state duty cycle, the bypass switching switch has completed the on / off switching, and the converter duty cycle has transitioned to the steady-state operating point. The distribution network obtains a voltage regulation operation state after a smooth switching, in which the load-side port voltage is stable within the preset qualified range.

[0097] This method was applied to a bidirectional voltage regulation device in a low-voltage distribution substation. The substation is powered by a 630 kVA 10 kV / 380 V distribution transformer. The inductor branch is a series filter inductor with an inductance value of 0.5 millihenries. The terminal samples the inductor current at 128 sampling points per power frequency cycle. The preset zero current threshold is 2 Amperes, and the preset duration threshold is 0.0005 seconds.

[0098] During a switch from bypass to buck mode, the terminal detected four consecutive sampling points with current values ​​of 1.8 amps, 1.5 amps, 1.2 amps, and 0.9 amps, all less than 2 amps, for a duration of 0.000624 seconds, which is greater than the threshold of 0.0005 seconds. The terminal was then determined to be in the zero current crossover range.

[0099] The terminal reads the 6-row, 10-column switch pre-action timing matrix, and starts parsing the control redundant protection switch to turn off from the first column. This is completed within 0.0002 seconds. The second and third columns are parsed sequentially to control the first grid-side switch and the first load-side switch to turn off, and the second grid-side switch and the second load-side switch to turn on. The time interval between each cycle is 0.001 seconds. All five branch switches to be operated are switched within 0.003 seconds. After receiving all feedback signals, a switching completion confirmation signal is generated.

[0100] At this point, the target steady-state duty cycle of the buck mode is 0.85, the pre-switching duty cycle reference value is 0.9, the difference is -0.05, the preset adjustment steps are 50, the single-step adjustment amount is -0.001, and it steps once every two switching cycles. In the first cycle, it remains unchanged at 0.9, and in the second cycle, it decreases to 0.899. After 100 switching cycles with a total duration of 0.002 seconds, the duty cycle smoothly decreases from 0.9 to 0.85.

[0101] The switching is performed within the zero current crossing range. The maximum inductor current at the moment of switching is only 1.8 amps. There are no voltage spikes or arcing. The duty cycle changes gradually, allowing the load-side voltage to smoothly transition from 220 volts to 207 volts without overshoot or oscillation, and it remains stable in the range of 198 volts to 235.4 volts.

[0102] This transformer substation has performed this type of switching more than 120 times in three consecutive months. Each time, the switching was completed within the zero current crossing range. The duty cycle was smoothly adjusted to the target value in a two-cycle step-by-step manner. No switching shocks or voltage sudden changes occurred, and the equipment operated stably and reliably.

[0103] Step 6: In the voltage regulation operation state after the disturbance-free switching, the voltage deviation between the load side port voltage signal and the preset voltage reference value is proportionally adjusted and superimposed on the target steady-state duty cycle to generate a real-time duty cycle command and output it to the bidirectional switching transistor, so that the load side port voltage is stabilized within the preset voltage qualified range.

[0104] In this embodiment of the invention, under the voltage regulation operation state after the disturbance-free switching, the voltage deviation between the load-side port voltage signal and the preset voltage reference value is proportionally adjusted and then superimposed on the target steady-state duty cycle to generate a real-time duty cycle command and output to the bidirectional switching transistor, so that the load-side port voltage is stabilized within the preset qualified voltage range. The process is as follows: The instantaneous voltage values ​​of the load-side port voltage are continuously collected at multiple sampling times, and the instantaneous voltage values ​​at multiple sampling times are subjected to mean filtering to obtain the real-time effective voltage value of the load-side port voltage. The duty cycle compensation amount is obtained by multiplying the voltage deviation between the real-time effective voltage value and the preset voltage reference value by the preset proportional gain coefficient. The duty cycle compensation is superimposed on the target steady-state duty cycle of the distribution network at the current moment to obtain the real-time duty cycle command. The real-time duty cycle command is converted into a pulse width modulation signal and output to the drive terminal of the bidirectional switch to adjust the conduction duty cycle of the bidirectional switch so that the real-time effective value of the load-side port voltage approaches the preset voltage reference value.

[0105] The voltage sampling module inside the terminal continuously samples the voltage signal at the load-side port at equal intervals with a fixed sampling frequency. At each sampling moment, an instantaneous voltage value is obtained. These instantaneous voltage values ​​are arranged in chronological order to form an instantaneous voltage sampling sequence.

[0106] The terminal obtains the instantaneous voltage values ​​corresponding to multiple sampling times before the current time from the instantaneous voltage sampling sequence, sums these multiple instantaneous voltage values ​​to obtain a total value, and then divides the total value by the total number of sampling points involved in the summation to obtain the average value of these instantaneous voltage values. This average value is the real-time effective value of the load-side port voltage after mean filtering.

[0107] In the above mean filtering process, the total number of sampling points involved in the accumulation is a fixed positive integer. This value is preset and stored inside the terminal. The terminal uses the same number of sampling points each time it calculates to ensure the consistency of the filtering effect.

[0108] The terminal internally stores a preset voltage reference value, which is a fixed voltage value representing the target voltage level that the load-side port voltage should reach under normal operating conditions. The terminal subtracts the preset voltage reference value from the real-time effective voltage value obtained through mean filtering; the difference between the two is the voltage deviation. When the real-time effective voltage value is greater than the preset voltage reference value, the voltage deviation is positive, indicating that the current load voltage is higher than the target value, and the output voltage needs to be reduced. When the real-time effective voltage value is less than the preset voltage reference value, the voltage deviation is negative, indicating that the current load voltage is lower than the target value, and the output voltage needs to be increased. When the real-time effective voltage value equals the preset voltage reference value, the voltage deviation is zero, indicating that the current load voltage has reached the target value and no adjustment is needed.

[0109] The terminal internally stores a preset proportional gain coefficient, a fixed positive number, used to linearly map the magnitude of the voltage deviation to the magnitude of the duty cycle adjustment. The terminal multiplies the voltage deviation by the preset proportional gain coefficient; the product is the duty cycle compensation amount, which represents the magnitude of duty cycle adjustment required to eliminate the voltage deviation. When the voltage deviation is positive, the duty cycle compensation amount is positive, indicating that the duty cycle needs to be increased to raise the output voltage. When the voltage deviation is negative, the duty cycle compensation amount is negative, indicating that the duty cycle needs to be decreased to lower the output voltage. When the voltage deviation is zero, the duty cycle compensation amount is zero, indicating that no duty cycle adjustment is required.

[0110] The terminal reads the target steady-state duty cycle of the distribution network at the current moment. This target steady-state duty cycle is the reference duty cycle value set by the distribution network to maintain voltage regulation operation after a seamless handover. The terminal adds the duty cycle compensation value to the target steady-state duty cycle value, that is, it adds the duty cycle compensation value to the target steady-state duty cycle to obtain a new duty cycle value, which is the real-time duty cycle command. When the duty cycle compensation value is positive, the real-time duty cycle command value is greater than the target steady-state duty cycle, instructing the bidirectional switch to operate at a larger conduction ratio to increase the output voltage. When the duty cycle compensation value is negative, the real-time duty cycle command value is less than the target steady-state duty cycle, instructing the bidirectional switch to operate at a smaller conduction ratio to decrease the output voltage. When the duty cycle compensation value is zero, the real-time duty cycle command value is equal to the target steady-state duty cycle, instructing the bidirectional switch to maintain the current conduction ratio.

[0111] The terminal transmits the real-time duty cycle command value to its internal pulse width modulation (PWM) signal generation circuit. This circuit contains a high-frequency counter that counts cyclically from zero to a fixed period, corresponding to the duration of one complete switching cycle. The PWM signal generation circuit converts the real-time duty cycle command value into a comparison threshold, which is equal to the period count multiplied by the real-time duty cycle command value. The high-frequency counter increments from zero within each switching cycle. When the current counter value is less than the comparison threshold, the PWM signal generation circuit outputs a high-level signal; when the current counter value is greater than or equal to the comparison threshold, it outputs a low-level signal. This forms a PWM signal whose high-level duration is equal to the ratio of the total switching cycle duration to the real-time duty cycle command value.

[0112] The pulse width modulation (PWM) signal generation circuit outputs the generated PWM signal to the drive terminal of the bidirectional switch via the drive line. Upon receiving the signal, the drive terminal controls the bidirectional switch to turn on during the high-level period and turn off during the low-level period, thus achieving operation according to the conduction ratio indicated by the real-time duty cycle command. After the bidirectional switch adjusts its conduction duty cycle according to the real-time duty cycle command, the output voltage of the AC / AC converter changes accordingly, and the real-time effective value of the load-side port voltage rises or falls accordingly, gradually approaching the preset voltage reference value. At the end of each switching cycle, the terminal repeats the entire process of sampling, mean filtering, deviation calculation, compensation calculation, command superposition, and PWM signal generation, forming a continuous closed-loop regulation process to ensure that the real-time effective value of the load-side port voltage remains stable near the preset voltage reference value.

[0113] The closed-loop voltage regulation method was applied to a bidirectional voltage regulation device in a low-voltage distribution area. The area is powered by a 630 kVA 10 kV / 380 V distribution transformer. The AC / AC converter is connected to the grid bus on the high-voltage side and the load line on the low-voltage side. The bidirectional switching tube has a switching frequency of 50 kHz.

[0114] The terminal samples the load-side voltage at 128 sampling points per power frequency cycle. The number of sampling points participating in the mean filtering is 128, corresponding to one complete power frequency cycle.

[0115] In buck mode operation, the target steady-state duty cycle is 0.85, the preset voltage reference value is 220V, and the proportional gain coefficient is 0.005. After sampling 128 instantaneous values ​​and averaging them, the real-time effective voltage value is 226V. Subtracting the reference value of 220V, the voltage deviation is +6V. Multiplying this by the proportional gain coefficient of 0.005 gives a duty cycle compensation of +0.03. This is superimposed on the target steady-state duty cycle of 0.85 to obtain the real-time duty cycle command of 0.88. The pulse width modulation signal generation circuit outputs a drive signal with a duty cycle of 88%. The bidirectional switching transistor operates according to this conduction ratio. After 10 power frequency cycles of closed-loop adjustment, the real-time effective voltage value gradually stabilizes from 226V to 221.2V, and the deviation is reduced to 1.2V. Subsequent continuous adjustment stabilizes the voltage between 219.8V and 220.2V, and the real-time duty cycle command stabilizes around 0.851.

[0116] In another boost mode, the real-time effective voltage is 208 volts, the voltage deviation is -12 volts, the compensation is -0.06, which is superimposed on the target steady-state duty cycle of 0.92 to obtain a real-time duty cycle command of 0.86. The output drive signal with a duty cycle of 86% is generated, and the voltage gradually rises from 208 volts to 219.5 volts.

[0117] Three consecutive months of operation records show that this closed-loop regulation method can continuously calculate the duty cycle compensation based on the real-time voltage deviation and update the real-time duty cycle command in various buck-boost modes. The load-side voltage is always maintained within ±2% of the preset reference value, and there is no voltage deviation or oscillation, so the power supply quality is fully guaranteed.

[0118] As can be seen from the above embodiments, the distribution network step-up / step-down seamless switching method provided by the present invention can generate accurate target operating mode commands by judging the over-limit of the grid-side port voltage and comparing it with the current operating mode logic. By combining the inductor current direction, amplitude and port voltage phase difference to construct a switching window prediction sequence, the optimal switching time window can be accurately determined. With the adjustment of the switch pre-action timing matrix and the pre-switching duty cycle reference value, the bypass switch switching is completed in the zero current crossing interval, and the switch smoothly transitions to the target steady-state duty cycle with a preset slope. This effectively eliminates voltage surges and current disturbances during the switching process, reduces the switching stress of the switching devices, and compensates the duty cycle in real time by adjusting the load-side voltage deviation ratio, so that the load-side voltage is stabilized within the qualified range. This comprehensively improves the smoothness of distribution network voltage regulation switching, power supply reliability and voltage regulation accuracy.

[0119] like Figure 2 The diagram shown is a functional block diagram of a distribution network step-up / step-down seamless switching system 100 provided in an embodiment of the present invention, including an operation mode decision module 101, a switching window prediction module 102, a switch timing arrangement module 103, a duty cycle pre-adjustment module 104, a seamless switching execution module 105, and a real-time voltage regulation control module 106.

[0120] In this embodiment, the functions of each module are as follows: The operation mode decision module 101 is used to determine the over-limit of the effective value of the voltage at the grid side port in the distribution network, and to logically compare the obtained voltage over-limit status identifier with the current operation mode of the distribution network to generate a target operation mode instruction. The switching window prediction module 102 is used to fuse and sort the direction and amplitude of the inductor current and the phase difference between the port voltages of the grid side and the load side in the distribution network, construct a switching window prediction sequence, and determine the optimal switching time window. The switch timing arrangement module 103 is used to arrange the pre-conduction state of the bypass switching switch in the distribution network into a switch pre-action timing matrix according to the target operation mode instruction within the optimal switching time window. The duty cycle pre-adjustment module 104 is used to calculate the pre-switching duty cycle reference value according to the voltage adjustment ratio relationship corresponding to the target operating mode command, and adjust the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value. The disturbanceless switching execution module 105 is used to perform on / off switching on each branch switch in the bypass switching switch according to the switch pre-action timing matrix when the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window. After the switching is completed, the duty cycle of the bidirectional switching tube is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to the preset slope, so as to obtain the voltage regulation operation state after disturbanceless switching. The real-time voltage regulation control module 106 is used to, in the voltage regulation operation state after disturbance-free switching, add the voltage deviation between the load-side port voltage signal and the preset voltage reference value to the target steady-state duty cycle after proportional adjustment, generate a real-time duty cycle command and output it to the bidirectional switching transistor, so that the load-side port voltage is stabilized within the preset voltage qualified range.

[0121] As can be seen from the above embodiments, the distribution network step-up / step-down seamless switching system provided by the present invention can generate accurate target operating mode commands by judging the over-limit of the grid-side port voltage and comparing it with the current operating mode logic. By combining the inductor current direction, amplitude and port voltage phase difference to construct a switching window prediction sequence, the optimal switching time window can be accurately determined. With the adjustment of the switch pre-action timing matrix and the pre-switching duty cycle reference value, the bypass switch switching is completed in the zero current crossing range, and the system smoothly transitions to the target steady-state duty cycle with a preset slope. This effectively eliminates voltage surges and current disturbances during the switching process, reduces the switching stress of the switching devices, and compensates the duty cycle in real time by adjusting the load-side voltage deviation ratio, so that the load-side voltage is stabilized within the qualified range. This comprehensively improves the smoothness of distribution network voltage regulation switching, power supply reliability and voltage regulation accuracy.

[0122] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for seamless switching of step-up and step-down voltage in a distribution network, characterized in that, The method includes: Step 1: Determine if the effective value of the voltage at the grid-side port in the distribution network exceeds the limit, and logically compare the obtained voltage over-limit status flag with the current operating mode of the distribution network to generate the target operating mode command; Step 2: In the distribution network, the direction and amplitude of the inductor current and the phase difference between the port voltages of the grid side and the load side are fused and sorted to construct a switching window prediction sequence and determine the optimal switching time window; Step 3: Within the optimal switching time window, based on the target operation mode instruction, arrange the pre-conduction states of the bypass switching switches in the distribution network into a switch pre-action timing matrix; Step 4: Calculate the pre-switching duty cycle reference value based on the voltage regulation ratio corresponding to the target operating mode command, and adjust the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value. Step 5: When the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window, according to the switch pre-action timing matrix, the on / off switching of each branch switch in the bypass switching switch is performed, and after the switching is completed, the duty cycle of the bidirectional switching tube is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to the preset slope, so as to obtain the voltage regulation operation state after the disturbanceless switching. Step 6: In the voltage regulation operation state after the disturbance-free switching, the voltage deviation between the load side port voltage signal and the preset voltage reference value is proportionally adjusted and superimposed on the target steady-state duty cycle to generate a real-time duty cycle command and output it to the bidirectional switching transistor, so that the load side port voltage is stabilized within the preset voltage qualified range.

2. The method for seamless switching of distribution network step-up / step-down voltage as described in claim 1, characterized in that, The process of determining whether the effective value of the grid-side port voltage in the distribution network exceeds the limit, and logically comparing the obtained voltage over-limit status identifier with the current operating mode of the distribution network to generate a target operating mode instruction is as follows: The root mean square operation is performed on each sampled value of the grid-side port voltage within one power frequency cycle to obtain the effective value of the grid-side port voltage. When the effective value is greater than the preset upper voltage threshold, a voltage exceeding the upper limit is generated; when the effective value is less than the preset lower voltage threshold, a voltage exceeding the lower limit is generated; when the effective value is between the preset lower voltage threshold and the preset upper voltage threshold, a voltage normal is generated, thus obtaining the voltage exceeding the limit status of the grid-side port voltage. The voltage over-limit status indicator is logically combined with the current operating mode indicator of the distribution network for judgment. The current operating mode indicator includes boost mode, buck mode and bypass direct mode. Use the generated mode instruction corresponding to the current running mode identifier as the target running mode instruction.

3. The method for seamless switching of step-up and step-down voltage in a distribution network as described in claim 2, characterized in that, The process of logically combining the voltage over-limit status identifier with the current operating mode identifier of the distribution network for discrimination is as follows: When the voltage over-limit status is indicated by the voltage over-limit flag and the current operating mode is not buck mode, a buck mode command is generated. When the voltage over-limit status is marked as the voltage under-limit status and the current operating mode is not boost mode, a boost mode command is generated. When the voltage over-limit status indicator is changed to the voltage normal status indicator, or when the voltage over-limit status indicator matches the current operating mode indicator, a command to maintain the current mode is generated.

4. The method for seamless switching of step-up and step-down voltage in a distribution network as described in claim 1, characterized in that, In the power distribution network, the direction and amplitude of the inductor current, as well as the phase difference between the port voltages on the grid side and the load side, are fused and sorted to construct a switching window prediction sequence and determine the optimal switching time window. The process is as follows: The instantaneous values ​​of the inductor current at multiple consecutive sampling times are obtained, the direction of the inductor current is determined according to the positive and negative polarities of the instantaneous values, and the absolute value of the instantaneous values ​​is taken as the amplitude of the inductor current. Calculate the time difference between the port voltages on the grid side and the load side in the distribution network at the zero crossing moment, and use the ratio of the time difference to the power frequency period of the distribution network as the phase difference between the port voltages on the grid side and the load side. The current inductor current direction, current amplitude, and port voltage phase difference are weighted and fused according to preset weighting coefficients to obtain the switching window evaluation value of the distribution network at the current moment. Based on the current time, slide forward a preset time window length, calculate the switching window evaluation value corresponding to each time within the preset time window length in turn, and sort each time in order from best to worst according to the switching window evaluation value to obtain the switching window prediction sequence. The optimal switching time window is obtained by selecting the time with the best evaluation value from the switching window prediction sequence as the center time and expanding outward with a preset width centered on the center time.

5. The method for seamless switching of step-up and step-down voltage in a distribution network as described in claim 1, characterized in that, Within the optimal switching time window, based on the target operating mode command, the pre-conduction states of the bypass switching switches in the distribution network are arranged into a switch pre-action timing matrix. The process is as follows: Read the current on / off status of each branch switch in the bypass switching switch in the distribution network; Query the pre-conduction target state of each branch switch corresponding to the target operation mode command from the preset switch state mapping table; Compare the current on / off state of each branch switch with the target state of pre-conduction to determine the target branch switch whose state needs to be changed and the corresponding target state. According to the preset switching sequence within the optimal switching time window, the target branch switches and their corresponding target states are arranged in the order of action to generate a switching action sequence. The switching action sequence is encoded into a binary matrix with each branch switch as the row and the time tick as the column, thus obtaining the switch pre-action timing matrix.

6. The method for seamless switching of step-up and step-down voltage in a distribution network as described in claim 1, characterized in that, The process of calculating the pre-switching duty cycle reference value based on the voltage regulation ratio corresponding to the target operating mode command, and adjusting the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value, is as follows: Decode the target operating mode command to identify the voltage regulation direction and voltage regulation amplitude corresponding to the target operating mode command. The voltage regulation direction includes either the voltage boosting direction or the voltage bucking direction, and the voltage regulation amplitude includes the voltage regulation ratio value corresponding to the target operating mode command. Calculate the pre-switching duty cycle reference value based on the voltage regulation direction and voltage regulation amplitude; The difference between the current duty cycle of the bidirectional switching transistor inside the AC / AC converter and the reference value of the pre-switching duty cycle is used as the duty cycle adjustment deviation. Based on the positive and negative directions of the duty cycle adjustment deviation, the duty cycle adjustment direction of the bidirectional switch is determined, and the duty cycle of the bidirectional switch is gradually changed according to the preset single adjustment step size until the duty cycle of the bidirectional switch reaches the pre-switching duty cycle reference value.

7. The method for seamless switching of distribution network step-up / step-down voltage as described in claim 6, characterized in that, The process of calculating the pre-switching duty cycle reference value based on the voltage regulation direction and voltage regulation amplitude is as follows: Obtain the high-voltage side port voltage sampling value and the low-voltage side port voltage sampling value inside the AC / AC converter; Based on the voltage regulation direction, one of the voltage sampling values ​​at the high-voltage side port and the low-voltage side port is determined as the reference voltage, and the other is determined as the target voltage. When the voltage regulation direction is the boost direction, the high voltage side port voltage sampling value is used as the reference voltage and the low voltage side port voltage sampling value is used as the target voltage. When the voltage regulation direction is the voltage reduction direction, the low-voltage side port voltage sampling value is used as the reference voltage and the high-voltage side port voltage sampling value is used as the target voltage. The ratio of the target voltage to the reference voltage is used as the voltage transfer ratio, and divided by the equivalent gain coefficient of the AC / AC converter in the current operating state, to obtain the pre-switching duty cycle reference value.

8. The method for seamless switching of step-up and step-down voltage in a distribution network as described in claim 1, characterized in that, When the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window, according to the switch pre-action timing matrix, the on / off switching of each branch switch in the bypass switching switch is performed. After the switching is completed, the duty cycle of the bidirectional switching transistor is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to the preset slope, so as to obtain the voltage regulation operation state after the disturbanceless switching. The process is as follows: The instantaneous value of the inductor current in the distribution network is compared with the preset zero current threshold. When the instantaneous value of the inductor current is less than or equal to the preset zero current threshold, it is determined that the inductor current has entered the zero current state, and the duration of the inductor current in the zero current state is recorded. When the duration is greater than or equal to the preset duration threshold, the inductor current is determined to be in the zero current crossover interval corresponding to the optimal switching time window. Within the zero current crossing range, the action sequence of each branch switch in the pre-action timing matrix of the switch is analyzed, and the on / off control signal of each branch switch is output sequentially according to the action order in the action sequence of each branch switch, so as to complete the on / off switching of all branch switches to be operated in the bypass switching switch. After detecting that all the switch to be operated has completed the on / off switching, the difference between the target steady-state duty cycle corresponding to the target operating mode command and the pre-switching duty cycle reference value is divided by the preset number of adjustment steps to obtain the single-step adjustment amount. According to the preset slope, the duty cycle of the bidirectional switching transistor is increased by a single-step adjustment amount in every two adjacent switching cycles until the duty cycle of the bidirectional switching transistor reaches the target steady-state duty cycle, thus obtaining the voltage regulation operation state after disturbance-free switching.

9. The method for seamless switching of step-up and step-down voltage in a distribution network as described in claim 1, characterized in that, In the voltage regulation operation state after the disturbance-free switching, the voltage deviation between the load-side port voltage signal and the preset voltage reference value is proportionally adjusted and then superimposed on the target steady-state duty cycle to generate a real-time duty cycle command, which is then output to the bidirectional switching transistor to stabilize the load-side port voltage within the preset qualified voltage range. The process is as follows: The instantaneous voltage values ​​of the load-side port voltage are continuously collected at multiple sampling times, and the instantaneous voltage values ​​at multiple sampling times are subjected to mean filtering to obtain the real-time effective voltage value of the load-side port voltage. The duty cycle compensation amount is obtained by multiplying the voltage deviation between the real-time effective voltage value and the preset voltage reference value by the preset proportional gain coefficient. The duty cycle compensation is superimposed on the target steady-state duty cycle of the distribution network at the current moment to obtain the real-time duty cycle command. The real-time duty cycle command is converted into a pulse width modulation signal and output to the drive terminal of the bidirectional switch to adjust the conduction duty cycle of the bidirectional switch so that the real-time effective value of the load-side port voltage approaches the preset voltage reference value.

10. A power distribution network step-up / step-down seamless switching system, characterized in that, A system for implementing a distribution network step-up / step-down seamless switching method according to any one of claims 1-9, the system comprising: The operation mode decision module is used to determine the over-limit of the effective value of the voltage at the grid side port in the distribution network, and to logically compare the obtained voltage over-limit status identifier with the current operation mode of the distribution network to generate the target operation mode instruction; The switching window prediction module is used to integrate and sort the direction and amplitude of inductor current and the phase difference between the port voltages of the grid side and the load side in the distribution network, construct the switching window prediction sequence, and determine the optimal switching time window. The switch timing arrangement module is used to arrange the pre-conduction states of the bypass switching switches in the distribution network into a switch pre-action timing matrix according to the target operation mode instruction within the optimal switching time window; The duty cycle pre-adjustment module is used to calculate the pre-switching duty cycle reference value based on the voltage adjustment ratio corresponding to the target operating mode command, and adjust the current duty cycle of the bidirectional switching transistor inside the AC / AC converter to the pre-switching duty cycle reference value. The bumpless switching execution module is used to perform on / off switching on each branch switch in the bypass switching switch according to the switch pre-action timing matrix when the inductor current in the distribution network is in the zero current crossing interval corresponding to the optimal switching time window. After the switching is completed, the duty cycle of the bidirectional switching transistor is gradually adjusted from the pre-switching duty cycle reference value to the target steady-state duty cycle corresponding to the target operating mode command according to the preset slope, so as to obtain the voltage regulation operation state after bumpless switching. The real-time voltage regulation control module is used to, in the voltage regulation operation state after disturbance-free switching, to proportionally adjust the voltage deviation between the load-side port voltage signal and the preset voltage reference value and add it to the target steady-state duty cycle, generate a real-time duty cycle command and output it to the bidirectional switching transistor, so that the load-side port voltage is stabilized within the preset voltage qualified range.

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