A power distribution network voltage out-of-limit management device and a control method thereof

Abstract

This invention relates to a voltage over-limit mitigation device and control method for power distribution networks. The device includes a voltage regulator and a transformer. The voltage regulator comprises three sets of switch pairs, two inductors, and two capacitors. Its input side is connected in parallel to the power supply side of the power distribution network, and its output side is connected in series to the load side via the transformer. When the device is activated, the output voltage of the AC / AC voltage regulator is calculated based on the current load voltage, the ideal load voltage, and the transformer turns ratio. The operating mode and switching control method of the AC / AC voltage regulator are determined based on the output voltage, thereby adjusting the load voltage to mitigate voltage over-limits. This invention enables flexible voltage increase and decrease regulation in power distribution networks, has strong short-circuit withstand capability, and features a simple structure, control system, and low cost.

Description

Technical Field

[0001] This invention relates to the field of power quality management technology for distribution networks, and in particular to a distribution network voltage over-limit management device and its control method. Background Technology

[0002] With the increasing use of distributed power sources and loads in power distribution networks, and the long transmission distances in remote areas, the problem of voltage exceeding limits on power lines is becoming increasingly prominent. Voltage exceeding limits can lead to reduced transmission efficiency, equipment malfunction, and even accidents such as equipment damage and personal injury. Existing voltage regulation devices mainly consist of back-to-back AC / DC rectifiers and DC / AC inverter modules, which are complex in structure and control, and have high costs.

[0003] CN115940185B discloses a series-parallel side coordinated control method for a UPQC topology. The structure includes series-parallel side transformers, filters, AC / DC rectifiers, DC / AC inverters, etc. When performing voltage compensation, coordinated control of the two converters is required, which makes the structure and control relatively complex and costly.

[0004] CN113141014B discloses an AC voltage regulating device and control method. The device includes an input terminal connected to the power grid, an input capacitor, an upper bridge arm, a lower bridge arm, an absorption module, and a discharge module. The total output voltage is controlled by adjusting the PWM duty cycle of the switching devices in the upper and lower bridge arms. This topology can only achieve voltage reduction and is difficult to handle low voltage boosting. In addition, the power required for voltage regulation in series input lines is large and the short-circuit withstand capability is poor. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a distribution network voltage over-limit control device and its control method, which can realize flexible voltage increase and decrease regulation of distribution network lines, strong short circuit resistance, and has a simple structure and control with low cost.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: a distribution network voltage over-limit control device is provided, including a voltage regulator and a transformer; the voltage regulator includes three sets of switch pairs, two inductors, and two capacitors, wherein the first end of the first switch pair is connected to the first end of the secondary side of the transformer and the first end of the first capacitor, the second end of the first switch pair is connected to the first end of the first inductor and the first end of the second switch pair, the second end of the second switch pair is connected to the first end of the second inductor, the second end of the first inductor is connected to the first end of the third switch pair, the second end of the third switch pair is connected to the first end of the primary side of the transformer and the first end of the second capacitor, the second end of the first capacitor, the second end of the second capacitor, and the second end of the second inductor are connected to the second end of the primary side of the transformer, and the first end and the second end of the secondary side of the transformer are respectively connected to the power supply side and the load side of the distribution network.

[0007] Furthermore, it also includes a switching combination used to bypass the voltage regulator and transformer when the effective value of the load-side voltage is within the set voltage range, and to engage the voltage regulator and transformer when the effective value of the load-side voltage exceeds the set voltage range.

[0008] Furthermore, the switching combination includes three switching switches, wherein the first terminal of the first switching switch is connected to the power supply side and the first terminal of the second switching switch, the second terminal of the first switching switch is connected to the load side and the second terminal of the third switching switch, the second terminal of the second switching switch is connected to the first terminal of the transformer secondary side, the first terminal of the first switch pair and the first terminal of the first capacitor, and the first terminal of the third switching switch is connected to the second terminal of the transformer secondary side.

[0009] Furthermore, the first switching switch is closed and the second and third switching switches are open to bypass the voltage regulator and transformer; the first switching switch is open and the second and third switching switches are closed to connect the voltage regulator and transformer.

[0010] Furthermore, the third switch pair is always on, while the first and second switch pairs are alternately on, to achieve load-side voltage regulation when the effective value of the load-side voltage is greater than or equal to the ideal value.

[0011] Furthermore, each switch pair includes two switch transistors with source interconnects.

[0012] Furthermore, the second switching transistors of the first switch pair and the second switching transistors of the second switch pair are complementary and conduct, while the first switching transistors of the third switch pair, the first switching transistor of the first switch pair, and the first switching transistor of the second switch pair are constantly on, so as to achieve load-side voltage regulation when the effective value of the load-side voltage is greater than or equal to the ideal value and the voltage across the first capacitor is less than zero.

[0013] Furthermore, the second switch pair is always on, while the first and third switch pairs are alternately turned on to regulate the load-side voltage when the effective value of the load-side voltage is less than the ideal value.

[0014] Furthermore, the second switching transistors of the first switch pair and the second switching transistors of the third switch pair are complementary and conduct, while the first switching transistors of the second switch pair, the first switching transistor of the first switch pair, and the first switching transistor of the third switch pair are always on, so as to achieve load-side voltage regulation when the effective value of the load-side voltage is less than the ideal value and the difference between the voltages across the first capacitor and the second capacitor is less than zero.

[0015] The present invention also provides a control method for a distribution network voltage over-limit mitigation device, applied to the device described above, comprising the following steps:

[0016] The difference between the effective value and the ideal value of the load-side voltage is monitored, and then the target output voltage of the voltage regulator is calculated based on the transformer turns ratio.

[0017] The input voltage across the first capacitor and the output voltage across the second capacitor are acquired in real time.

[0018] When the target output voltage is greater than or equal to zero, the third switch pair is set to be constantly on, while the first and second switch pairs are alternately on.

[0019] When the target output voltage is less than zero, the second switch pair is set to be constantly on, while the first and third switch pairs are alternately on.

[0020] Furthermore, the duty cycle of the first switch pair is obtained by PI regulation of the difference between the effective value of the target output voltage and the measured output voltage.

[0021] Furthermore, it also includes the step of setting the transformer ratio according to the voltage regulation range so that the duty cycle of the first switch pair is within the set range.

[0022] Beneficial effects

[0023] By adopting the above-mentioned technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0024] This invention constructs an AC / AC voltage regulation topology comprising three sets of source-interconnected bidirectional power switch pairs to achieve AC voltage compensation and regulation. This reduces device size and hardware costs, avoids voltage fluctuation losses in the DC link, and provides faster voltage regulation response, adapting to the dynamic management needs of distribution network voltage exceeding limits. The series isolation transformer not only achieves electrical isolation between the compensation voltage and the power grid, improving device operational safety, but also enhances the device's versatility for different power distribution scenarios by matching the voltage regulation range of different distribution networks through the transformer ratio. The structure of the bidirectional switch pairs is naturally adapted to the bidirectional current characteristics of AC power, eliminating the need for additional reverse switches, simplifying the topology and reducing control complexity.

[0025] This invention addresses two over-limit scenarios in distribution networks: undervoltage and overvoltage. By considering the polarity difference of capacitor voltage during the positive and negative half-cycles of AC voltage, it designs differentiated switch conduction logic. This logic enables voltage rise compensation during undervoltage and voltage drop compensation during overvoltage, comprehensively resolving over-limit issues caused by excessively high or low voltage in distribution networks and effectively improving power supply quality. Corresponding control strategies are designed for the positive and negative half-cycles of AC voltage to ensure continuous voltage regulation throughout the entire cycle, without altering the grid voltage phase and avoiding additional interference to the load power supply. By maintaining a fixed switch constant on-state, control variables are reduced, lowering control complexity while ensuring accurate output of the compensation voltage. This supports the safe and stable operation of the distribution network, providing reliable power supply for industrial production, residential electricity consumption, and other scenarios. Attached Figure Description

[0026] Figure 1 This is a topology diagram of the six-switch AC / AC voltage regulator in the first and second embodiments of the present invention;

[0027] Figure 2 This is a control block diagram of the voltage regulator in the forward voltage regulation mode in the first and second embodiments of the present invention;

[0028] Figure 3 This is a control block diagram of the voltage regulator in reverse voltage regulation mode in the first and second embodiments of the present invention;

[0029] Figure 4 This is a flowchart of the second embodiment of the present invention. Detailed Implementation

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] The first embodiment of the present invention relates to a distribution network voltage over-limit control device based on a six-switch AC / AC voltage regulator. The device topology includes a six-switch AC / AC voltage regulator and a transformer. The input side of the AC / AC voltage regulator is connected in parallel to the power supply side, and the output side is connected in series to the load side through the transformer.

[0032] Voltage over-limit mitigation device topology as follows Figure 1 As shown, the AC / AC voltage regulator includes 3 groups of 6 switches in total, and input and output capacitors C. in C out There are two control inductors, L1 and L2. Switches S1 and S2 form the first switch pair, switches S3 and S4 form the second switch pair, and switches S5 and S6 form the third switch pair. The sources of the two switching transistors in each switch pair are interconnected.

[0033] The first terminal of the first switch pair is connected to the first terminal of the secondary side of the transformer and the capacitor C, respectively. in The first terminal is connected, and the second terminal of the first switch pair is connected to the first terminal of inductor L1 and the first terminal of the second switch pair, respectively. The second terminal of the second switch pair is connected to the first terminal of inductor L2, and the second terminal of inductor L1 is connected to the first terminal of the third switch pair. The second terminal of the third switch pair is connected to the first terminal of the primary side of the transformer and the capacitor C, respectively. out The first terminal is connected to capacitor C. in The second terminal, capacitor C outThe second end of the transformer and the second end of the inductor L2 are connected to the second end of the primary side of the transformer. The first and second ends of the secondary side of the transformer are connected to the power supply side and the load side of the distribution network, respectively.

[0034] In some preferred embodiments, the voltage over-limit control device can be automatically switched on and off to the line at appropriate times using a switching switch. The specific control method is as follows: detect the effective value of the load-side voltage; if the voltage is within the national standard allowable voltage range, bypass the voltage over-limit control device; if the voltage exceeds the national standard allowable voltage range, activate the voltage over-limit control device.

[0035] DS1~DS3 are the device switching switches. The device detects the effective value of the load-side voltage. If the voltage is within the national standard allowable voltage range, switch DS1 is closed and switches DS2 and DS3 are opened to bypass the voltage over-limit control device. If the voltage exceeds the national standard allowable voltage range, switch DS1 is opened and switches DS2 and DS3 are closed to activate the voltage over-limit control device.

[0036] After the device is connected to the line, the secondary voltage of the transformer is calculated based on the current and ideal load voltage values. The AC / AC output voltage is then calculated from the secondary voltage and the transformer turns ratio. The operating mode and switching control method of the AC / AC regulator are determined based on the AC / AC output voltage, and the duty cycle of each switch is obtained through voltage closed-loop control.

[0037] When putting the device into operation, since AC / AC voltage regulation does not change the voltage phase, the following only describes the voltage amplitude adjustment method.

[0038] The current voltage amplitude on the load side is detected as U. R0 If the ideal voltage amplitude of the load is U R1 The series transformer is expected to regulate the voltage to be

[0039] (1)

[0040] When the desired load voltage amplitude increases, U t <0; When the desired load voltage amplitude decreases, U t >0.

[0041] Based on the transformer turns ratio (N:1), the expected output voltage of the AC / AC converter can be calculated as follows:

[0042] (2)

[0043] According to U out_ref The sign indicates the AC / AC operating mode of the six-switch system. When U... out_ref When U > 0, the AC / AC operates in forward voltage regulation mode. out_refWhen the value of N is less than 0, the AC / AC operates in reverse voltage regulation mode. The value of N is selected based on the voltage regulation range, and it is necessary to consider ensuring that the duty cycle of the AC / AC switch is appropriate. The duty cycle in forward voltage regulation mode is approximately NU. t / U R0 The duty cycle in reverse voltage regulation mode is approximately NU. t / (NU t -U R0 ).

[0044] In forward voltage regulation mode, switches S5 and S6 are always on. The duty cycle d of switches S1 and S2 is... p From the expected value of the output voltage U out_ref The difference between the measured value and the actual value is obtained through PI adjustment. The PI parameters are selected based on Matlab / Simulink simulation tests to ensure that the system has no oscillations or divergence, and the dynamic response overshoot is ≤10%. The duty cycles of S3 and S4 are 1-d. p The duty cycle is modulated by a PWM switch to obtain the switching signal. The modulation method is as follows: when the input voltage u... in When u > 0, switches S2 and S4 are always on, while S1 and S3 are complementary and on. in When the value is less than 0, switches S1 and S3 are always on, while S2 and S4 are complementary and on. The control block diagram is as follows: Figure 2 As shown.

[0045] In reverse voltage regulation mode, switches S3 and S4 are always on. The duty cycles d of switches S1 and S2 are... n byU out_ref The difference between the measured value and the actual value is obtained through PI adjustment. The PI parameters are selected based on Matlab / Simulink simulation tests to ensure that the system has no oscillations or divergence, and the dynamic response overshoot is ≤10%. The duty cycles of S5 and S6 are 1-d. n The duty cycle is modulated by a PWM switch to obtain the switching signal. The modulation method is: when the input voltage is subtracted from the output voltage (u... in -u out When (u) ≥ 0, switches S2 and S6 are always on, while S1 and S5 are complementary and on. in -u out When ) < 0, switches S1 and S5 are always on, while S2 and S6 are complementary and on. The control block diagram is as follows: Figure 3 As shown.

[0046] This device is suitable for both single-phase and three-phase voltage regulation. It is applicable to both low-voltage and medium-voltage lines. When used in medium-voltage lines, an isolation transformer must be added to the input side. This isolation transformer must withstand the power frequency withstand voltage test and lightning impulse voltage as specified in national standards, and the neutral point on the secondary side must be reliably grounded. The insulation class and withstand voltage capacity of the six-switch AC / AC voltage regulator also need to be upgraded accordingly.

[0047] The second embodiment of the present invention relates to a control method for a distribution network voltage over-limit mitigation device based on a six-switch AC / AC voltage regulator, wherein the voltage over-limit mitigation device includes an AC / AC voltage regulator and a transformer, the input side of the AC / AC voltage regulator is connected in parallel to the power supply side, and the output side is connected in series to the load side through the transformer.

[0048] like Figure 1 As shown, the AC / AC voltage regulator includes 3 groups of 6 switches in total, and input and output capacitors C. in C out There are two control inductors, L1 and L2. Switches S1 and S2 form the first switch pair, switches S3 and S4 form the second switch pair, and switches S5 and S6 form the third switch pair. The sources of the two switching transistors in each switch pair are interconnected.

[0049] The first terminal of the first switch pair is connected to the first terminal of the secondary side of the transformer and the capacitor C, respectively. in The first terminal is connected, and the second terminal of the first switch pair is connected to the first terminal of inductor L1 and the first terminal of the second switch pair, respectively. The second terminal of the second switch pair is connected to the first terminal of inductor L2, and the second terminal of inductor L1 is connected to the first terminal of the third switch pair. The second terminal of the third switch pair is connected to the first terminal of the primary side of the transformer and the capacitor C, respectively. out The first terminal is connected to capacitor C. in The second terminal, capacitor C out The second end of the transformer and the second end of the inductor L2 are connected to the second end of the primary side of the transformer. The first and second ends of the secondary side of the transformer are connected to the power supply side and the load side of the distribution network, respectively.

[0050] like Figure 4 As shown, the specific steps include:

[0051] The difference between the effective value and the ideal value of the load-side voltage is monitored, and then the target output voltage of the voltage regulator is calculated based on the transformer turns ratio.

[0052] Real-time acquisition of capacitance C in The input voltage at both ends, and the capacitor C out Output voltage at both ends;

[0053] When the target output voltage is greater than or equal to zero, the third switch is set to be always on. At this time, if the input voltage is greater than or equal to zero, switches S2 and S4 are set to be always on, and switches S1 and S3 are set to be complementary and conduct. If the input voltage is less than zero, switches S1 and S3 are set to be always on, and switches S2 and S4 are set to be complementary and conduct.

[0054] When the target output voltage is less than zero, the second switch is set to be always on. At this time, if the difference between the input voltage and the output voltage is greater than or equal to zero, switches S2 and S6 are set to be always on, and switches S1 and S5 are set to be complementary and conduct. If the input voltage is less than zero, switches S1 and S5 are set to be always on, and switches S2 and S6 are set to be complementary and conduct.

[0055] In some preferred embodiments, the voltage over-limit control device can be automatically switched on and off to the line at appropriate times using a switching switch. The specific control method is as follows: detect the effective value of the load-side voltage; if the voltage is within the national standard allowable voltage range, bypass the voltage over-limit control device; if the voltage exceeds the national standard allowable voltage range, activate the voltage over-limit control device.

[0056] DS1~DS3 are the device switching switches. The device detects the effective value of the load-side voltage. If the voltage is within the national standard allowable voltage range, switch DS1 is closed and switches DS2 and DS3 are opened to bypass the voltage over-limit control device. If the voltage exceeds the national standard allowable voltage range, switch DS1 is opened and switches DS2 and DS3 are closed to activate the voltage over-limit control device.

[0057] When putting the device into operation, since AC / AC voltage regulation does not change the voltage phase, the following only describes the voltage amplitude adjustment method.

[0058] The current voltage amplitude on the load side is detected as U. R0 If the ideal voltage amplitude of the load is U R1 The series transformer is expected to regulate the voltage to be

[0059] (1)

[0060] When the load voltage amplitude increases, U t <0; when the load voltage amplitude decreases, U t >0.

[0061] Based on the transformer turns ratio (N:1), the expected output voltage of the AC / AC converter can be calculated as follows:

[0062] (2)

[0063] According to U out_ref The sign indicates the AC / AC operating mode of the six-switch system. When U... out_ref When U > 0, the AC / AC operates in forward voltage regulation mode. out_ref When the value of N is less than 0, the AC / AC operates in reverse voltage regulation mode. The value of N is selected based on the voltage regulation range, ensuring that the duty cycle of the AC / AC switch is appropriate (e.g., within the range of 0.2~0.8). The duty cycle in forward voltage regulation mode is approximately NU. t / UR0 The duty cycle in reverse voltage regulation mode is approximately NU. t / (NU t -U R0 ).

[0064] In forward voltage regulation mode, switches S5 and S6 are always on. The duty cycle d of switches S1 and S2 is... p From the expected value of the output voltage U out_ref The difference between the measured value and the actual value is obtained through PI adjustment. The PI parameters are selected based on Matlab / Simulink simulation tests to ensure that the system has no oscillations or divergence, and the dynamic response overshoot is ≤10%. The duty cycles of S3 and S4 are 1-d. p The duty cycle is modulated by a PWM switch to obtain the switching signal. The modulation method is as follows: when the input voltage u... in When u > 0, switches S2 and S4 are always on, while S1 and S3 are complementary and on. in When the value is less than 0, switches S1 and S3 are always on, while S2 and S4 are complementary and on. The control block diagram is as follows: Figure 2 As shown.

[0065] In reverse voltage regulation mode, switches S3 and S4 are always on. The duty cycles d of switches S1 and S2 are... n byU out_ref The difference between the measured value and the actual value is obtained through PI adjustment. The PI parameters are selected based on Matlab / Simulink simulation tests to ensure that the system has no oscillations or divergence, and the dynamic response overshoot is ≤10%. The duty cycles of S5 and S6 are 1-d. n The duty cycle is modulated using PWM (Pulse Width Modulation) to obtain the switching signal. The modulation method is as follows: when the input voltage is subtracted from the output voltage (u... in -u out When (u) ≥ 0, switches S2 and S6 are always on, while S1 and S5 are complementary and on. in -u out When ) < 0, switches S1 and S5 are always on, while S2 and S6 are complementary and on. The control block diagram is as follows: Figure 3 As shown.

Claims

1. A distribution network voltage over-limit control device, characterized in that, It includes a voltage regulator and a transformer; the voltage regulator includes three sets of switch pairs, two inductors, and two capacitors. The first end of the first switch pair is connected to the first end of the secondary side of the transformer and the first end of the first capacitor, respectively. The second end of the first switch pair is connected to the first end of the first inductor and the first end of the second switch pair, respectively. The second end of the second switch pair is connected to the first end of the second inductor. The second end of the first inductor is connected to the first end of the third switch pair. The second end of the third switch pair is connected to the first end of the primary side of the transformer and the first end of the second capacitor, respectively. The second ends of the first capacitor, the second capacitor, and the second inductor are connected to the second end of the primary side of the transformer. The first and second ends of the secondary side of the transformer are connected to the power supply side and the load side of the distribution network, respectively. The third switch pair is always on, while the first and second switch pairs are alternately on to achieve load-side voltage regulation when the effective value of the load-side voltage is greater than or equal to the ideal value. The second switch pair is always on, while the first and third switch pairs are alternately on to regulate the load-side voltage when the effective value of the load-side voltage is less than the ideal value.

2. The apparatus according to claim 1, characterized in that, It also includes a switching combination, which is used to bypass the voltage regulator and transformer when the effective value of the load side voltage is within the set voltage range, and to connect the voltage regulator and transformer when the effective value of the load side voltage exceeds the set voltage range.

3. The apparatus according to claim 2, characterized in that, The switching combination includes three switching switches. The first terminal of the first switching switch is connected to the power supply side and the first terminal of the second switching switch. The second terminal of the first switching switch is connected to the load side and the second terminal of the third switching switch. The second terminal of the second switching switch is connected to the first terminal of the transformer secondary side, the first terminal of the first switch pair, and the first terminal of the first capacitor. The first terminal of the third switching switch is connected to the second terminal of the transformer secondary side.

4. The apparatus according to claim 3, characterized in that, When the first switching switch is closed and the second and third switching switches are open, the voltage regulator and transformer are bypassed; when the first switching switch is open and the second and third switching switches are closed, the voltage regulator and transformer are connected.

5. The apparatus according to claim 1, characterized in that, Each switch pair includes two switch transistors with source interconnects.

6. A control method for a distribution network voltage over-limit mitigation device, characterized in that, Applied to the apparatus as described in any one of claims 1-5, comprising the following steps: The difference between the effective value and the ideal value of the load-side voltage is monitored, and then the target output voltage of the voltage regulator is calculated based on the transformer turns ratio. The input voltage across the first capacitor and the output voltage across the second capacitor are acquired in real time. When the target output voltage is greater than or equal to zero, the third switch pair is set to be constantly on, while the first and second switch pairs are alternately on. When the target output voltage is less than zero, the second switch pair is set to be constantly on, while the first and third switch pairs are alternately on.

7. The control method according to claim 6, characterized in that, The duty cycle of the first switch pair is obtained by PI regulation through the difference between the effective value of the target output voltage and the measured output voltage.

8. The control method according to claim 7, characterized in that, It also includes the step of setting the transformer ratio according to the voltage regulation range so that the duty cycle of the first switch pair is within the set range.

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