A high-voltage SVG power unit DC voltage control system

Abstract

The application relates to the technical field of cascade H-bridge SVG, and discloses a high-voltage SVG power unit DC voltage control system, which comprises a main controller unit and 3n H-bridge power units; a power unit control board comprises a DC voltage sampling circuit, an IGBT driving circuit, an IGBT driving power supply and a power unit control chip; the main controller unit acquires the DC voltage of each H-bridge power unit and a power unit current; when the power unit current is greater than or equal to a light-load constant value, the main controller unit determines a PWM duty ratio and sends the PWM duty ratio to each H-bridge power unit; when the power unit current is less than the light-load constant value, the main controller unit determines the difference between the DC voltage of each H-bridge power unit and the average value of the DC voltages, and determines the driving voltage target value of each H-bridge power unit based on a regulator and the difference; and the application ensures the reliability of the DC voltage balance control of each H-bridge power unit.

Description

Technical Field

[0001] This invention relates to the field of cascaded H-bridge SVG technology, and more specifically, to a DC voltage control system for a high-voltage SVG power unit. Background Technology

[0002] With the development of power systems, the demand for dynamic reactive power compensation, voltage stability support, and harmonic suppression in power grids is becoming increasingly urgent. High-voltage static var generators (SVG) are widely used in wind / photovoltaic power plants, industrial distribution networks, and urban power supply systems due to their advantages such as fast response speed, wide adjustment range, and low harmonic pollution. The cascaded H-bridge topology is the architecture of the SVG, enabling high-voltage output and expansion through modular design.

[0003] Existing patent CN107888091A discloses a method for controlling the voltage balance of a cascaded H-bridge rectifier DC capacitor. The method selects the required output voltage phasor by the magnitude of the DC-side capacitor voltage, so that the capacitor voltage can reach balance as quickly as possible. However, a modulation voltage that is in phase with the output current is superimposed on the H-bridge, which causes the modulation voltage and the output current to generate a different active power for each H-bridge. If a small current is output, the superimposed modulation voltage cannot generate active power, resulting in the cascaded H-bridge rectifier DC capacitor voltage failing to reach balance.

[0004] Therefore, it is necessary to design a high-voltage SVG power unit DC voltage control system to solve the problems existing in the current technology. Summary of the Invention

[0005] In view of this, the present invention proposes a DC voltage control system for a high-voltage SVG power unit, which aims to solve the problem that when the existing technology outputs a small current, the superimposed modulation voltage cannot generate active power, resulting in the inability to balance the DC capacitor voltage of the cascaded H-bridge rectifier.

[0006] This invention proposes a DC voltage control system for a high-voltage SVG power unit, comprising:

[0007] The main controller unit and 3n H-bridge power units, where n is a positive integer, each H-bridge power unit includes a power unit control board and an H-bridge, and the power unit control board and the H-bridge are connected;

[0008] The power unit control board includes a DC voltage sampling circuit, an IGBT driving circuit, an IGBT driving power supply, and a power unit control chip. The power unit control chip is connected to the DC voltage sampling circuit, the IGBT driving circuit, and the IGBT driving power supply, respectively.

[0009] The main controller unit acquires the DC voltage and current of each H-bridge power unit and determines the average DC voltage. When the current of the power unit is greater than or equal to the light load setting, the main controller unit determines the PWM duty cycle and sends it to each H-bridge power unit. When the current of the power unit is less than the light load setting, the main controller unit determines the difference between the DC voltage and the average DC voltage of each H-bridge power unit. Based on the regulator and the difference, the main controller unit determines the target value of the drive voltage of each H-bridge power unit. Each power unit control board adjusts the drive voltage of the IGBT based on the target value of the drive voltage.

[0010] Furthermore, the main controller unit acquires the DC voltage of each H-bridge power unit based on optical fiber signals, and determines the current of each phase power unit through a current sensor.

[0011] Furthermore, when the power unit current is greater than or equal to the light load setting, the main controller unit determines the PWM duty cycle based on the inverter current loop and sets the target value of the drive voltage of each power unit control board to the maximum positive voltage of the IGBT.

[0012] Furthermore, when the current of the power unit is greater than or equal to the light load setting, the method further includes: the main controller unit determines the PWM correction value of each H-bridge power unit based on the superimposed active vector voltage algorithm, and uses the superposition result of the PWM correction value and the PWM value as the duty cycle of the IGBT.

[0013] Furthermore, when the power unit current is less than the light load setting, the main controller unit determines the PWM duty cycle based on the inverter current loop and sets the PWM correction value of each power unit control board to 0.

[0014] Furthermore, the high-voltage SVG power unit DC voltage control system includes: when the power unit current is less than the light load set value, the main controller unit determines the difference between the DC voltage of each H-bridge power unit and the average DC voltage, and uses the difference as the DC voltage deviation, and the main controller unit calculates the target value of the drive voltage of the power unit control board based on the DC voltage deviation of the H-bridge power units.

[0015] Furthermore, the high-voltage SVG power unit DC voltage control system includes: the regulator is used to reduce the target value of the drive voltage of the H-bridge power unit when the DC voltage is greater than the DC voltage threshold.

[0016] Furthermore, the high-voltage SVG power unit DC voltage control system includes: the parameters of the regulator are tuned based on the DC voltage deviation of the H-bridge power unit and the driving voltage range of the IGBT.

[0017] Furthermore, the high-voltage SVG power unit DC voltage control system includes: the IGBT drive power supply of the power unit control board is a forward power supply or a flyback power supply, and the duty cycle of the IGBT drive power supply is controlled by the power unit control chip.

[0018] Furthermore, the high-voltage SVG power unit DC voltage control system includes: the light-load setting value is determined based on the rated current.

[0019] Compared with the prior art, the beneficial effects of this invention are as follows: It adopts an architecture where a main controller unit and 3n H-bridge power units work collaboratively. Each H-bridge power unit integrates a power unit control board and an H-bridge. The power unit control board carries a DC voltage sampling circuit, an IGBT drive circuit, an IGBT drive power supply, and a power unit control chip. The main controller unit acquires the DC voltage and power unit current of each H-bridge power unit in real time and calculates the average DC voltage. When the power unit current is greater than or equal to the light load setpoint, the main controller unit directly determines the PWM duty cycle and sends it to each H-bridge power unit, based on mature modulation logic. The system achieves DC voltage balance. When the current of a power unit is less than the light load setpoint, the main controller unit calculates the difference between the DC voltage of each H-bridge power unit and the average DC voltage, and determines the target value of the drive voltage in conjunction with the regulator. Each power unit control board adjusts the drive voltage of the IGBT according to the target value of the drive voltage. By changing the conduction loss of the IGBT, DC voltage balance is achieved, avoiding the risk of PWM modulation voltage equalization failure under low current conditions. Moreover, it can be adapted to various cascaded H-bridge high-voltage SVGs without changing the circuit topology, taking into account the voltage equalization effect and control accuracy across the entire load range, thereby improving the voltage balance capability of the system. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A circuit schematic diagram of a DC voltage control system for a high-voltage SVG power unit provided in an embodiment of the present invention;

[0022] Figure 2 The circuit schematic diagram of the H-bridge power unit provided in the embodiment of the present invention;

[0023] Figure 3 This is a control principle diagram of a forward power supply for IGBT driving provided in an embodiment of the present invention;

[0024] Figure 4 The control principle diagram of the IGBT drive power supply provided in the embodiment of the present invention is a flyback power supply. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] See Figure 1-4 As shown in some embodiments of this application, a high-voltage SVG power unit DC voltage control system includes:

[0028] The main controller unit and 3n H-bridge power units, where n is a positive integer, each H-bridge power unit includes a power unit control board and an H-bridge, and the power unit control board and the H-bridge are connected.

[0029] The power unit control board includes a DC voltage sampling circuit, an IGBT drive circuit, an IGBT drive power supply, and a power unit control chip. The power unit control chip is connected to the DC voltage sampling circuit, the IGBT drive circuit, and the IGBT drive power supply, respectively.

[0030] The main controller unit acquires the DC voltage and current of each H-bridge power unit and determines the average DC voltage. When the power unit current is greater than or equal to the light load setting, the main controller unit determines the PWM duty cycle and sends it to each H-bridge power unit. When the power unit current is less than the light load setting, the main controller unit determines the difference between the DC voltage and the average DC voltage of each H-bridge power unit. Based on the regulator and the difference, the main controller unit determines the target value of the drive voltage for each H-bridge power unit. Each power unit control board adjusts the drive voltage of the IGBT based on the target value of the drive voltage.

[0031] Specifically, the main controller unit communicates with 3n H-bridge power units via fiber optic signals. Within the power unit control board of each H-bridge power unit, a DC voltage sampling circuit collects the DC voltage of the H-bridge in real time and feeds the DC voltage sampling signal back to the power unit control chip, which then transmits it to the main controller unit via fiber optic. Simultaneously, the main controller unit acquires the power unit current and calculates the average DC voltage of all H-bridge power units. When the power unit current is greater than or equal to the light load setpoint, the PWM duty cycle is determined based on the inverter current loop and sent to each H-bridge power unit via fiber optic signal. The power unit control chip is an FPGA chip. After receiving the PWM duty cycle, the power unit control chip sends IGBT control signals to the IGBT drive circuit, driving the IGBTs in the H-bridge to switch on and off, thereby achieving reactive power compensation. This meets the real-time requirements of high-voltage SVG dynamic reactive power compensation while avoiding harmonic interference, thus ensuring the power quality of the system. When the current of the power unit is less than the light load setpoint, the main controller unit determines the difference between the DC voltage fed back by each H-bridge power unit and the calculated average DC voltage. The main controller unit inputs all the differences to the regulator to determine the target value of the drive voltage for each H-bridge power unit. The regulator can be a proportional-integral controller or other controllers. After receiving the target value of the drive voltage, the power unit control chip on the power unit control board changes the drive voltage by adjusting the output of the IGBT drive power supply and the control signal of the IGBT drive circuit. By adjusting the IGBT drive voltage, the losses of each H-bridge power unit are changed, rather than relying on the active power exchange between the output current and the modulation voltage. This avoids the risk of not being able to generate active power and the DC voltage being difficult to balance under light load conditions, effectively ensuring the DC voltage consistency and system operation stability of the high-voltage SVG within the load range.

[0032] Specifically, the main controller unit determines the PWM duty cycle based on the inverter current loop, determines the PWM correction value of each H-bridge power unit based on the superimposed active vector voltage algorithm, and uses the superposition result of the PWM correction value and the PWM value as the duty cycle of the IGBT.

[0033] The light load setting is set to 10% of the rated current, which is the rated output current of each H-bridge power unit. This can be dynamically adjusted based on the actual current conditions. The main controller unit acquires the DC voltages U1, U2, ... Un of each H-bridge power unit and calculates the average DC voltage Uavg. When the power unit current is greater than or equal to the light load setting, the main controller unit determines the PWM correction value for each H-bridge power unit based on the superimposed active vector voltage algorithm. The superposition result of the PWM correction value and the PWM value is used as the duty cycle of the IGBT. Furthermore, the control board of each power unit sets the target drive voltage to the maximum positive voltage of the IGBT, thereby achieving balanced DC voltage control. Currently, the method of adjusting for conditions greater than or equal to the light load setting using the superimposed active vector voltage algorithm is relatively mature. However, when the power unit current is less than the light load setting, the existing superimposed modulation voltage cannot generate active power, making it impossible to balance the DC capacitor voltage of the cascaded H-bridge rectifier.

[0034] Specifically, when the current of the power unit is less than the light load setting, the main controller unit determines the difference between the DC voltage and the average DC voltage of each H-bridge power unit, namely ΔU1, ΔU2, ... ΔUn, where ΔUi = Ui - Uavg, and sends each difference to the regulator. The regulator's output is then limited, and the limited result Ugei is used as the target value of the drive voltage for each H-bridge power unit. The regulator's function is to reduce the target value of the drive voltage for H-bridge power units with excessively high DC voltage. The regulator can be a proportional controller or a proportional-integral controller, and there is no specific limitation. Its corresponding parameters are tuned based on the DC voltage deviation of the H-bridge power unit and the drive voltage range of the IGBT.

[0035] For example, when selecting a proportional controller, its parameters are set as follows:

[0036] Kp1=-0.5(Ugemax–Ugemin) / ΔU;

[0037] Ugei=Kp1*ΔUi+0.5(Ugemax+Ugemin);

[0038] Ugei = Max(Ugei, Ugemin);

[0039] Ugei = Min(Ugei, Ugemax);

[0040] Where Kp1 represents the proportional coefficient of the proportional controller, Ugemax represents the maximum positive voltage of the IGBT, Ugemin represents the minimum positive voltage of the IGBT, ΔUi represents the difference between the DC voltage and the average DC voltage of the i-th H-bridge power unit, and Ugei represents the target value of the IGBT drive voltage of the i-th H-bridge power unit. Typically, the drive voltage range of the IGBT is 12-15V. In this embodiment, Ugemin is 12V, Ugemax is 15V, and ΔU is selected as 5% of the rated DC voltage. For a 10kV system, it is usually taken as 37.5V.

[0041] For example, when selecting a proportional-integral controller, its parameters are set as follows:

[0042] Kp2=-0.5(Ugemax–Ugemin) / ΔU;

[0043] Ki = Kp2 * Ts;

[0044] Usi(t) = Usi(t-1) + Ki * ΔUi(t);

[0045] Ugei(t)=Kp2*ΔUi(t)+Usi(t)+0.5(Ugemax+Ugemin);

[0046] Ugei(t) = Max(Ugei, Ugemin);

[0047] Ugei(t) = Min(Ugei, Ugemax);

[0048] Where: Kp2 represents the proportional coefficient of the proportional-integral controller, Ugemax represents the maximum positive voltage of the IGBT, Ugemin represents the minimum positive voltage of the IGBT, Ts is the control period, which is calculated once per power frequency cycle in this embodiment and is selected as 20ms, Ki represents the integral coefficient of the proportional-integral controller, Usi(t) is the integral term of the i-th H-bridge power unit in the current control period t, Usi(t-1) represents the integral term of the i-th H-bridge power unit in the previous control period t-1, Ugei(t) represents the target value of the IGBT drive voltage of the i-th H-bridge power unit in the control period t, ΔUi(t) represents the difference between the DC voltage and the average DC voltage of the i-th H-bridge power unit in the control period t. The drive voltage range of the IGBT is generally 12-15V. In this embodiment, Ugemin is 12V, Ugemax is 15V, and ΔU is selected as 5% of the rated DC voltage. For a 10kV system, it is usually taken as 37.5V.

[0049] Specifically, the PWM correction value is the PWM duty cycle adjustment amount corresponding to the active component additionally added by the main controller unit to achieve DC voltage balance among the H-bridge power units. The IGBT drive power supply of the power unit control board is an isolated power supply with adjustable output voltage, i.e., a forward or flyback power supply. When the IGBT drive power supply is a forward power supply, Vin represents the input voltage of the drive power supply, the transformer turns ratio is N:1, and V- represents the negative voltage of the drive power supply. Therefore, the drive duty cycle is calculated by the drive power supply control program.

[0050] PWM-Duty=(Ugei+V-)*N / Vin;

[0051] Wherein, PWM-Duty represents the drive duty cycle, and Ugei represents the target value of the IGBT drive voltage of the i-th H-bridge power unit.

[0052] When the IGBT drive power supply is a flyback power supply, Vin represents the input voltage of the drive power supply, the transformer turns ratio is N:1, and V- represents the negative voltage of the drive power supply. Therefore, the drive duty cycle is calculated by the drive power supply control program.

[0053] PWM-Duty=N(Ugei+V-) / [Vin+N(Ugei+V-)];

[0054] Wherein, PWM-Duty represents the drive duty cycle, and Ugei represents the target value of the IGBT drive voltage of the i-th H-bridge power unit.

[0055] Specifically, the circuit composed of the drive power supply can also be other isolated DC / DC circuits. The duty cycle of the IGBT drive power supply, also known as the drive duty cycle, is controlled by the power unit control chip to achieve dynamic IGBT drive power supply voltage. By dynamically adjusting the IGBT drive power supply voltage, DC voltage balance control of each H-bridge power unit is achieved.

[0056] In summary, the beneficial effects of this invention are as follows: It employs an architecture where a main controller unit and 3n H-bridge power units work collaboratively. Each H-bridge power unit integrates a power unit control board and an H-bridge. The power unit control board carries a DC voltage sampling circuit, an IGBT drive circuit, an IGBT drive power supply, and a power unit control chip. The main controller unit acquires the DC voltage and power unit current of each H-bridge power unit in real time and calculates the average DC voltage. When the power unit current is greater than or equal to the light-load setpoint, the main controller unit directly determines the PWM duty cycle and sends it to each H-bridge power unit, based on mature modulation logic. To achieve DC voltage balance, when the current of a power unit is less than the light load setpoint, the main controller unit calculates the difference between the DC voltage of each H-bridge power unit and the average DC voltage, and determines the target value of the drive voltage in conjunction with the regulator. Each power unit control board adjusts the drive voltage of the IGBT according to the target value of the drive voltage. By changing the conduction loss of the IGBT, DC voltage balance is achieved, avoiding the risk of PWM modulation voltage equalization failure under low current conditions. Moreover, it can be adapted to various cascaded H-bridge high-voltage SVGs without changing the circuit topology, taking into account the voltage equalization effect and control accuracy across the entire load range, thereby improving the voltage balance capability of the system.

[0057] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program goods according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A DC voltage control system for a high-voltage SVG power unit, characterized in that, include: The system includes a main controller unit and 3n H-bridge power units, where n is a positive integer. Each H-bridge power unit includes a power unit control board and an H-bridge, and the power unit control board and the H-bridge are connected. The power unit control board includes a DC voltage sampling circuit, an IGBT driving circuit, an IGBT driving power supply, and a power unit control chip. The power unit control chip is connected to the DC voltage sampling circuit, the IGBT driving circuit, and the IGBT driving power supply, respectively. The main controller unit acquires the DC voltage and current of each H-bridge power unit and determines the average DC voltage. When the current of the power unit is greater than or equal to the light load setting, the main controller unit determines the PWM duty cycle and sends it to each H-bridge power unit. When the current of the power unit is less than the light load setting, the main controller unit determines the difference between the DC voltage and the average DC voltage of each H-bridge power unit. Based on the regulator and the difference, the main controller unit determines the target value of the drive voltage of each H-bridge power unit. Each power unit control board adjusts the drive voltage of the IGBT based on the target value of the drive voltage.

2. The high-voltage SVG power unit DC voltage control system according to claim 1, characterized in that, include: The main controller unit acquires the DC voltage of each H-bridge power unit based on optical fiber signals and determines the current of each phase power unit through a current sensor.

3. The high-voltage SVG power unit DC voltage control system according to claim 2, characterized in that, When the current of the power unit is greater than or equal to the light load setting, the main controller unit determines the PWM duty cycle based on the inverter current loop and sets the target value of the drive voltage of each power unit control board to the maximum positive voltage of the IGBT.

4. The high-voltage SVG power unit DC voltage control system according to claim 3, characterized in that, When the current of the power unit is greater than or equal to the light load setting, the method further includes: the main controller unit determines the PWM correction value of each H-bridge power unit based on the superimposed active vector voltage algorithm, and uses the superposition result of the PWM correction value and the PWM value as the duty cycle of the IGBT.

5. The high-voltage SVG power unit DC voltage control system according to claim 4, characterized in that, When the current of the power unit is less than the light load setting, the main controller unit determines the PWM duty cycle based on the inverter current loop and sets the PWM correction value of each power unit control board to 0.

6. The high-voltage SVG power unit DC voltage control system according to claim 5, characterized in that, include: When the current of the power unit is less than the light load setting, the main controller unit determines the difference between the DC voltage of each H-bridge power unit and the average DC voltage, and uses the difference as the DC voltage deviation. The main controller unit then calculates the target value of the drive voltage of the power unit control board based on the DC voltage deviation of the H-bridge power units.

7. The high-voltage SVG power unit DC voltage control system according to claim 6, characterized in that, include: The regulator is used to reduce the target value of the drive voltage of the H-bridge power unit when the DC voltage is greater than the DC voltage threshold.

8. The high-voltage SVG power unit DC voltage control system according to claim 7, characterized in that, include: The parameters of the regulator are tuned based on the DC voltage deviation of the H-bridge power unit and the driving voltage range of the IGBT.

9. The high-voltage SVG power unit DC voltage control system according to claim 8, characterized in that, include: The IGBT drive power supply of the power unit control board is either a forward power supply or a flyback power supply, and the duty cycle of the IGBT drive power supply is controlled by the power unit control chip.

10. The high-voltage SVG power unit DC voltage control system according to claim 9, characterized in that, include: The light load setting is determined based on the rated current.

Images