Energy storage type flexible direct current converter module and energy storage type flexible direct current converter

Abstract

The invention provides an energy storage type flexible direct current converter module and an energy storage type flexible direct current converter. According to the energy storage type flexible direct-current conversion module, the flexible direct-current conversion sub-module is connected with the energy storage unit through the non-isolated bidirectional direct-current converter, the energy storage unit and the flexible direct-current conversion sub-module are effectively integrated, the utilization rate of the energy storage unit is improved, and the economical efficiency, the flexibility and the reliability of a power grid system are improved through component sharing and modular design; meanwhile, when the capacitor voltage of the flexible direct current conversion sub-module is larger than a first preset voltage threshold value, the flexible direct current conversion sub-module charges the energy storage unit, and when the capacitor voltage of the flexible direct current conversion sub-module is smaller than a second preset voltage threshold value, the energy storage unit discharges the flexible direct current conversion sub-module. The non-isolated bidirectional direct-current converter is independently controlled, decoupling of energy storage voltage and capacitor voltage is achieved, and the energy storage unit has the strong active supporting capacity of deep discharge for the flexible direct current conversion sub-module.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current converters, and in particular to an energy storage type flexible direct current converter module and an energy storage type flexible direct current converter. Background Art

[0002] Flexible DC transmission technology based on modular multilevel converter (MMC) has the advantages of low harmonic content, flexible control, independent regulation of active and reactive power, etc. It has important applications in high-voltage DC transmission, grid interconnection, island power supply, and new energy grid connection. In recent years, with the continuous development and application of flexible DC transmission technology, the power grid has also undergone profound changes and faced new challenges, which are specifically reflected in: First, the proportion of new energy continues to increase, and the system inertia is significantly reduced, resulting in a decrease in stability when the power grid is disturbed, and it is necessary to configure equipment with active support capabilities for assistance; Second, new energy is random and volatile, and it is necessary to configure energy storage / energy consumption equipment to smooth out new energy fluctuations and achieve fault crossing. The current mainstream technical solution is to support the power grid by configuring active support equipment, but there are generally problems such as poor technical and economic performance, high system complexity, and difficulty in coordination between new equipment. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides an energy storage type flexible DC commutation module, the energy storage type flexible DC commutation module comprising: a flexible DC commutation submodule, a non-isolated bidirectional DC converter and an energy storage unit;

[0004] The flexible DC commutation submodule is connected in parallel with the non-isolated bidirectional DC converter;

[0005] The non-isolated bidirectional DC converter is also connected to the energy storage unit;

[0006] The non-isolated bidirectional DC converter is used to control the flexible DC commutation submodule to be disconnected from the energy storage unit when the energy storage type flexible DC commutation module is in normal operation, and to control the flexible DC commutation submodule to charge the energy storage unit when the capacitor voltage of the flexible DC commutation submodule is greater than a first preset voltage threshold, and to control the energy storage unit to discharge to the flexible DC commutation submodule when the capacitor voltage of the flexible DC commutation submodule is less than a second preset voltage threshold, so as to maintain the stability of the capacitor voltage of the flexible DC commutation submodule.

[0007] Optionally, the non-isolated bidirectional DC converter is further connected to an external controller;

[0008] The non-isolated bidirectional DC converter is also used to receive different control signals sent by an external controller, and based on the different control signals, adjust the magnitude of the conduction current of the switch tube in the non-isolated bidirectional DC converter to control the magnitude of the charging and discharging current between the flexible DC commutation submodule and the energy storage unit.

[0009] Optionally, the flexible DC commutation submodule is a half-bridge submodule, and the half-bridge submodule includes: a first switch tube, a second switch tube and a capacitor;

[0010] The first switch tube and the second switch tube are connected in series to form a commutation bridge arm, and the commutation bridge arm is connected in parallel with the capacitor.

[0011] Optionally, when the first switch tube is turned on and the second switch tube is turned off, the half-bridge sub-module is in a sub-module input state; when the first switch tube is turned off and the second switch tube is turned on, the half-bridge sub-module is in a sub-module cut-off state; when the first switch tube and the second switch tube are turned off at the same time, the half-bridge sub-module is in a sub-module locked state.

[0012] Optionally, the flexible DC commutation submodule is a full-bridge submodule, and the full-bridge submodule includes: a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a capacitor;

[0013] The first switch tube and the second switch tube are connected in series to form a first bridge arm, the third switch tube and the fourth switch tube are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are respectively connected in parallel with the capacitor.

[0014] Optionally, the non-isolated bidirectional DC converter comprises: a DC conversion upper bridge arm, a DC conversion lower bridge arm and an energy storage inductor;

[0015] The DC conversion upper bridge arm and the DC conversion lower bridge arm are connected in series to form a DC conversion bridge arm;

[0016] The midpoint of the DC bridge arm is connected to the energy storage inductor;

[0017] The DC conversion bridge arm is connected to the flexible DC commutation submodule and the energy storage unit respectively, and the energy storage inductor is also connected to the energy storage unit.

[0018] Optionally, the output end of the DC conversion upper bridge arm is connected to the input end of the DC conversion lower bridge arm and the first end of the energy storage inductor;

[0019] The input end of the DC conversion upper bridge arm is connected to the positive DC end of the flexible DC commutation submodule, the second end of the energy storage inductor is connected to the positive pole of the energy storage unit, and the output end of the DC conversion lower bridge arm is respectively connected to the negative DC end of the flexible DC commutation submodule and the negative pole of the energy storage unit.

[0020] Optionally, when the upper bridge arm of the DC conversion is turned on, the flexible DC commutation submodule is turned on with the energy storage unit, and the flexible DC commutation submodule charges the energy storage inductor and the energy storage unit; when the upper bridge arm of the DC conversion is turned off, the flexible DC commutation submodule is disconnected from the energy storage unit, and the energy storage inductor charges the energy storage unit;

[0021] When the lower bridge arm of the DC conversion is turned on, the flexible DC commutation submodule is disconnected from the energy storage unit, and the energy storage unit discharges to the energy storage inductor; when the lower bridge arm of the DC conversion is turned off, the flexible DC commutation submodule is turned on from the energy storage unit, and the energy storage inductor and the energy storage unit discharge to the flexible DC commutation submodule simultaneously.

[0022] Optionally, the output end of the DC conversion upper bridge arm is connected to the input end of the DC conversion lower bridge arm and the first end of the energy storage inductor;

[0023] The input end of the upper bridge arm of the DC conversion is connected to the positive DC end of the flexible DC commutation submodule, the second end of the energy storage inductor is respectively connected to the negative DC end of the flexible DC commutation submodule and the positive pole of the energy storage unit, and the output end of the lower bridge arm of the DC conversion is connected to the negative pole of the energy storage unit.

[0024] Optionally, when the upper bridge arm of the DC conversion is turned on, the flexible DC commutation submodule is turned on with the energy storage inductor, and the flexible DC commutation submodule charges the energy storage inductor; when the upper bridge arm of the DC conversion is turned off, the flexible DC commutation submodule is disconnected with the energy storage inductor, and the energy storage inductor charges the energy storage unit;

[0025] When the bridge arm under the DC conversion is turned on, the flexible DC commutator module is disconnected from the energy storage inductor, and the energy storage unit discharges to the energy storage inductor; when the bridge arm under the DC conversion is turned off, the flexible DC commutator module is turned on from the energy storage inductor, and the energy storage inductor discharges to the flexible DC commutator module.

[0026] Based on the same inventive concept, the present invention also provides an energy storage type flexible DC converter, which includes multiple parallel bridge arms; the connection points of the multiple bridge arms serve as the DC ends of the converter, and the bridge arms include multiple series-connected energy storage type flexible DC converter modules as described above.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides an energy storage type flexible direct current commutation module and an energy storage type flexible direct current converter. The energy storage type flexible direct current commutation module connects the flexible direct current commutation module with the energy storage unit by adopting a non-isolated bidirectional direct current converter, effectively integrates the energy storage unit with the flexible direct current commutation module, improves the utilization rate of the energy storage unit, and adopts component sharing and modular design to improve the economy and flexible reliability of the power grid system, and reduce the complexity of the system. At the same time, when the capacitor voltage of the flexible direct current commutation module is greater than the first preset voltage threshold, the flexible direct current commutation module charges the energy storage unit, and when the capacitor voltage of the flexible direct current commutation module is less than the second preset voltage threshold, the energy storage unit discharges to the flexible direct current commutation module, independently controls the non-isolated bidirectional direct current converter, realizes the decoupling of the energy storage voltage and the capacitor voltage, enables the energy storage unit to have a strong active support capability for deep discharge of the flexible direct current commutation module, and avoids the problem of difficulty in coordination between the newly added energy storage unit and the flexible direct current commutation module.

[0029] The energy storage flexible DC converter effectively integrates the energy storage unit with the flexible DC commutation sub-module through a non-isolated bidirectional DC converter, thereby improving the utilization rate of the energy storage unit. It also adopts component sharing and modular design to avoid configuring active support devices to support the power grid, thereby improving the economy and flexibility and reliability of the power grid system. At the same time, by independently controlling the non-isolated bidirectional DC converter, it avoids the problem of difficulty in coordination between new devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of an energy storage type flexible DC converter module provided by the present invention;

[0031] Figure 2 A schematic diagram of a half-bridge submodule provided by the present invention;

[0032] Figure 3 A schematic diagram of a full-bridge submodule provided by the present invention;

[0033] Figure 4 A schematic diagram of a non-isolated bidirectional DC converter provided by the present invention;

[0034] Figure 5 A schematic diagram of another energy storage type flexible DC converter module provided by the present invention;

[0035] Figure 6 A schematic diagram of charging and discharging of an energy storage type flexible DC converter module provided by the present invention;

[0036] Figure 7 A schematic diagram of charging and discharging of another energy storage type flexible DC converter module provided by the present invention;

[0037] Figure 8 A schematic diagram of charging and discharging of another energy storage type flexible DC converter module provided by the present invention;

[0038] Fig. 9 A schematic diagram of charging and discharging of another energy storage type flexible DC converter module provided by the present invention;

[0039] Fig.10 A schematic diagram of another energy storage type flexible DC converter module provided by the present invention;

[0040] Fig.11 A schematic diagram of another non-isolated bidirectional DC converter provided by the present invention;

[0041] Fig.12 A schematic diagram of another energy storage type flexible DC converter module provided by the present invention;

[0042] Fig.13 A schematic diagram of charging and discharging of another energy storage type flexible DC converter module provided by the present invention;

[0043] Fig.14 A schematic diagram of charging and discharging of another energy storage type flexible DC converter module provided by the present invention;

[0044] Fig.15 A schematic diagram of charging and discharging of another energy storage type flexible DC converter module provided by the present invention;

[0045] Fig.16 A schematic diagram of charging and discharging of another energy storage type flexible DC converter module provided by the present invention;

[0046] Fig.17 A schematic diagram of another energy storage type flexible DC converter module provided by the present invention. DETAILED DESCRIPTION

[0047] Embodiment 1:

[0048] Figure 1 A schematic diagram of an energy storage type flexible DC converter module provided by the present invention is shown in FIG. Figure 1As shown, the energy storage type flexible DC commutation module may include: a flexible DC commutation submodule 101, a non-isolated bidirectional DC converter 102 and an energy storage unit 103; the flexible DC commutation submodule 101 is connected in parallel with the non-isolated bidirectional DC converter 102; the non-isolated bidirectional DC converter 102 is also connected to the energy storage unit 103; the non-isolated bidirectional DC converter is used to control the flexible DC commutation submodule 101 to be disconnected from the energy storage unit 103 when the energy storage type flexible DC commutation module is in normal operation, control the flexible DC commutation submodule 101 to charge the energy storage unit 103 when the capacitor voltage of the flexible DC commutation submodule 101 is greater than a first preset voltage threshold, and control the energy storage unit 103 to discharge to the flexible DC commutation submodule 101 when the capacitor voltage of the flexible DC commutation submodule 101 is less than a second preset voltage threshold, so as to maintain the stability of the capacitor voltage of the flexible DC commutation submodule 101.

[0049] Among them, the flexible direct current commutation submodule can be a flexible direct current MMC (Modular Multilevel Converter) submodule, referred to as a flexible direct current submodule, and the non-isolated bidirectional direct current converter 102 can also be called a non-isolated bidirectional DC-DC (Direct-Current to Direct-Current, direct current-direct current) converter, referred to as a DC-DC converter. The first preset voltage threshold is greater than the second preset voltage threshold. The first preset voltage threshold can be the rated voltage of the capacitor in the flexible direct current commutation submodule, and can also be greater than the rated voltage of the capacitor. For example, the first preset voltage threshold can be 120%, 110% or 107% of the rated voltage of the capacitor, and can also be less than the rated voltage of the capacitor. For example, in general, in order to prevent voltage spikes from damaging the flexible direct current commutation submodule, the first preset voltage threshold can be set to 70% to 80% of the rated voltage of the capacitor. The second preset voltage threshold can be the minimum operating voltage of the capacitor in the flexible DC commutation sub-module, which is generally 20%-30% of the rated voltage of the capacitor, and can also be greater than the minimum operating voltage of the capacitor. For example, when the minimum operating voltage of the capacitor is 30% of the rated voltage of the capacitor, the second preset voltage threshold can be greater than 30% of the rated voltage of the capacitor.

[0050] It should be noted that by detecting the capacitor voltage of the energy storage type flexible DC converter module, it is determined whether the energy storage type flexible DC converter module is in normal operation. When the energy storage type flexible DC converter module is in normal operation, the non-isolated bidirectional DC converter 102 can control the flexible DC converter module 101 to be disconnected from the energy storage unit 103, and the energy storage unit 103 does not play a role, and does not affect the normal operation of the flexible DC converter module 101. When the energy storage type flexible DC converter module is in abnormal operation, the flexible DC converter module 101 and the energy storage unit 103 are connected through the non-isolated bidirectional DC converter 102, and the energy storage unit is charged or discharged. The abnormal operation may include that the capacitor voltage of the flexible DC converter module 101 is greater than the first preset voltage threshold, and the capacitor voltage of the flexible DC converter module 101 is less than the second preset voltage threshold.

[0051] The energy storage type flexible direct current commutation module of the present invention effectively integrates the flexible direct current commutation submodule with the energy storage unit, has the ability of autonomous energy dissipation and power support, and some devices are shared with the structural support components, which reduces the configuration of additional equipment and improves the overall economy of the system. The energy storage unit is connected in parallel to the capacitor side via a DC-DC converter, the energy storage voltage and the capacitor voltage of the flexible direct current submodule can be decoupled, the energy storage (i.e., the energy storage unit) and the flexible direct current (i.e., the flexible direct current commutation submodule) are controlled independently, the energy storage can achieve deep discharge, and can quickly respond to system requirements, with high energy conversion efficiency, and at the same time, avoids the problem of difficulty in coordination between the newly added energy storage unit and the flexible direct current commutation submodule.

[0052] Optionally, the non-isolated bidirectional DC converter 102 is also connected to an external controller; the non-isolated bidirectional DC converter 102 is also used to receive different control signals sent by the external controller, and based on the different control signals, adjust the conduction current of the switch tube in the non-isolated bidirectional DC converter 102 to control the charging and discharging current between the flexible DC commutation submodule 101 and the energy storage unit 103.

[0053] Among them, the external controller can be a closed-loop feedback control device, a PI (Proportional-Integral) controller or a PID (Proportional-Integral-Derivative) controller, and the control signal can be a PWM (Pulse Width Modulation) signal, a frequency modulation signal or a response control signal, etc.

[0054] It should be noted that when the energy storage type flexible DC converter module is in abnormal operation (i.e., the capacitor voltage of the flexible DC converter module 101 is greater than the first preset voltage threshold, or the capacitor voltage of the flexible DC converter module 101 is less than the second preset voltage threshold), the external controller sends different control signals to the non-isolated bidirectional DC converter 102, and the non-isolated bidirectional DC converter 102 adjusts the magnitude of the conduction current of the switch tube in the non-isolated bidirectional DC converter 102 based on the different control signals. The flexible DC submodule and the energy storage unit of the energy storage type flexible DC converter module proposed in the present invention are completely decoupled and independently controlled. Therefore, the working principle of the flexible DC converter is consistent with that of the conventional flexible DC. By receiving different control signals, the charging and discharging power of the energy storage is controlled by independently controlling the magnitude and direction of the charging and discharging current, thereby improving the strong active support capability of the energy storage unit for the deep discharge of the flexible DC converter module, and the energy storage unit absorbs the redundant energy of the flexible DC converter module.

[0055] The above technical solution integrates the energy storage unit and the flexible DC submodule into one, forming an energy storage-type flexible DC converter topology with active support and energy dissipation capabilities. The overall performance of the system is improved, and component sharing is highly economical. At the same time, a DC-DC converter is used to decouple the energy storage voltage from the flexible DC submodule voltage. The energy storage and the flexible DC are controlled flexibly and independently, the energy storage can be deeply discharged, and the utilization rate is high.

[0056] Figure 2 A schematic diagram of a half-bridge submodule provided by the present invention is shown in FIG. Figure 2 As shown, the flexible DC commutation submodule 101 can be a half-bridge submodule, which includes: a first switch tube T1, a second switch tube T2 and a capacitor C; the first switch tube T1 and the second switch tube T2 are connected in series to form a commutation bridge arm, and the commutation bridge arm is connected in parallel with the capacitor.

[0057] When the first switch tube T1 is turned on and the second switch tube T2 is turned off, the half-bridge submodule is in a submodule input state; when the first switch tube T1 is turned off and the second switch tube T2 is turned on, the half-bridge submodule is in a submodule cut-off state; when the first switch tube T1 and the second switch tube T2 are turned off at the same time, the half-bridge submodule is in a submodule locked state. The first switch tube T1 and the second switch tube T2 can be IGBT (Insulated Gate Bipolar Transistor, insulated gate bipolar transistor), IGCT (Integrated Gate-Commutated Thyristor, integrated gate commutated thyristor) or thyristor, etc.

[0058] It should be noted that if Figure 2The half-bridge submodule shown may further include a first access terminal P and a second access terminal N. The first access terminal P and the second access terminal N may be used to connect to an external power supply.

[0059] For example, T1-T2 can be IGBT tubes, D1-D2 can be anti-parallel diodes, C can be a flexible submodule capacitor, and T1, D1, T2, D2 and C form a half-bridge MMC flexible submodule (i.e., half-bridge submodule). Figure 2 Taking the half-bridge submodule shown in the figure as an example, T1 is turned on and T2 is turned off, which is the soft direct current submodule input state; T1 is turned off and T2 is turned on, which is the soft direct current submodule cut-off state; T1 and T2 are turned off at the same time, which is the submodule locked state.

[0060] Figure 3 A schematic diagram of a full-bridge submodule provided by the present invention is shown in FIG. Figure 3 As shown, the flexible DC commutation submodule 101 is a full-bridge submodule, and the full-bridge submodule includes: a first switch tube T1, a second switch tube T2, a third switch tube T3, a fourth switch tube T4 and a capacitor C; the first switch tube T1 and the second switch tube T2 are connected in series to form a first bridge arm, the third switch tube T3 and the fourth switch tube T4 are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are respectively connected in parallel with the capacitor C.

[0061] The first switch tube T1, the second switch tube T2, the third switch tube T3 and the fourth switch tube T4 may be IGBTs, IGCTs or thyristors, etc. The full bridge submodule may also include a first access terminal P and a second access terminal N, which may be used to connect to an external power supply.

[0062] It should be noted that when T1 and T4 are turned on and T2 and T3 are turned off, or when T1 and T4 are turned off and T2 and T3 are turned on, the flexible direct current sub-module is in the on-state; when T1 and T2 are turned off and T3 and T4 are turned on, or when T1 and T2 are turned on and T3 and T4 are turned off, the flexible direct current sub-module is in the off-state; when T1 to T4 are turned off at the same time, the sub-module is in the locked state.

[0063] For example, T1-T4 may be IGBT tubes, D1-D4 may be anti-parallel diodes, C may be a flexible submodule capacitor, and T1-T4, D1-D4 and C may constitute a full-bridge MMC flexible submodule (ie, a full-bridge submodule).

[0064] Optionally, the non-isolated bidirectional DC converter 102 includes: a DC conversion upper bridge arm, a DC conversion lower bridge arm and an energy storage inductor; the DC conversion upper bridge arm and the DC conversion lower bridge arm are connected in series to form a DC conversion bridge arm; the midpoint of the DC conversion bridge arm is connected to the energy storage inductor; the DC conversion bridge arm is respectively connected to the flexible DC commutation sub-module 101 and the energy storage unit 103, and the energy storage inductor is also connected to the energy storage unit 103.

[0065] Among them, the switching devices of the DC conversion upper bridge arm and the DC conversion lower bridge arm can use IGCT or thyristor in addition to IGBT.

[0066] It should be noted that when the flexible direct current commutation submodule 101 is a full-bridge submodule, the control method of the flexible direct current commutation submodule can adopt the control method of the full-bridge submodule in the DC converter in the prior art. The control method of the full-bridge submodule in the DC converter is widely used in the art, and the control method of the full-bridge submodule is not specifically described in the present invention. By turning on or off the DC conversion upper bridge arm and the DC conversion lower bridge arm, the energy storage inductor is charged or discharged, and the energy storage unit voltage is decoupled from the capacitor voltage of the flexible direct current commutation submodule. The energy storage unit and the flexible direct current commutation submodule are controlled independently, and the energy storage unit can achieve deep discharge, and can quickly respond to system requirements, with high energy conversion efficiency.

[0067] Optionally, the output end of the DC conversion upper bridge arm is connected to the input end of the DC conversion lower bridge arm and the first end of the energy storage inductor; the input end of the DC conversion upper bridge arm is connected to the positive DC end of the flexible DC commutation sub-module 101, the second end of the energy storage inductor is connected to the positive pole of the energy storage unit 103, and the output end of the DC conversion lower bridge arm is respectively connected to the negative DC end of the flexible DC commutation sub-module 101 and the negative pole of the energy storage unit 103.

[0068] Among them, when the upper bridge arm of the DC conversion is turned on, the flexible DC commutation submodule 101 is turned on with the energy storage unit 103, and the flexible DC commutation submodule 101 charges the energy storage inductor and the energy storage unit 103; when the upper bridge arm of the DC conversion is turned off, the flexible DC commutation submodule 101 is disconnected from the energy storage unit 103, and the energy storage inductor charges the energy storage unit 103; when the lower bridge arm of the DC conversion is turned on, the flexible DC commutation submodule 101 is disconnected from the energy storage unit 103, and the energy storage unit 103 discharges to the energy storage inductor; when the lower bridge arm of the DC conversion is turned off, the flexible DC commutation submodule 101 is turned on with the energy storage unit 103, and the energy storage inductor and the energy storage unit 103 discharge to the flexible DC commutation submodule 101 at the same time.

[0069] For example, Figure 4 As shown, Figure 4 A schematic diagram of a non-isolated bidirectional DC converter provided by the present invention, wherein the DC conversion upper bridge arm may include a fifth switch tube T5, the DC conversion lower bridge arm may include a sixth switch tube T6, D5-D6 are anti-parallel diodes, L may be an energy storage inductor, T4, D4, T5, D5 and L constitute a DC-DC converter, the anti-parallel diode D5 is anti-parallel to the fifth switch tube T5, and the anti-parallel diode D6 is anti-parallel to the sixth switch tube T6.

[0070] The fifth switch tube T5 and the sixth switch tube T6 may be IGBTs, IGCTs or thyristors.

[0071] For example, by Figure 2 The half-bridge submodule shown is similar to the above Figure 4 The non-isolated bidirectional DC converter shown in FIG. Figure 5 The energy storage type flexible DC converter module shown in the figure, Figure 5 A schematic diagram of another energy storage type flexible DC commutation module provided by the present invention, wherein the first switch tube T1 and the second switch tube T2 are connected in series to form a commutation bridge arm, the fifth switch tube T5 and the sixth switch tube T6 are connected in series to form a DC conversion bridge arm, the commutation bridge arm and the capacitor C are respectively connected in parallel with the DC conversion bridge arm, the energy storage inductor L and the energy storage unit E are connected in series to form an energy storage branch, and the energy storage branch is connected in parallel with the sixth switch tube T6. The energy storage inductor in the DC-DC converter of the type ① energy storage type flexible DC commutation module topology plays a role in assisting the energy exchange between the two sides: Figure 6 As shown, T5 remains off, and when T4 is on, the potential difference between the DC side and the energy storage side of the MMC submodule falls on the energy storage inductor L, and the electric energy is converted into magnetic field energy and stored in the inductor (i.e., T4=1, T5=0, MMC→energy storage charging, where "1" represents switch on and "0" represents switch off); Figure 7 As shown, after T4 is turned off, D5 is the inductor continuous current, converting the magnetic field energy in the inductor into electrical energy to charge the energy storage device (i.e., T4=0, T5=0, MMC→energy storage charging); Figure 8 As shown, when T4 is turned off and T5 is turned on, the voltage on the energy storage group side drops on both sides of the inductor L, causing the inductor to store energy, while the DC side voltage of the MMC is stabilized by C (i.e., T4 = 0, T5 = 1, energy storage → MMC discharge); Fig. 9 As shown, after T5 is turned off, the inductor and the energy storage device jointly charge the MMC DC side, and the energy obtained on the DC side is the sum of the energy of the inductor and the energy storage unit (ie, T4=0, T5=0, energy storage→MMC discharge).

[0072] For example, by Figure 3 The full bridge submodule shown is the same as the above Figure 4 The non-isolated bidirectional DC converter shown in FIG. Fig.10The energy storage type flexible DC converter module shown in the figure, Fig.10 A schematic diagram of another energy storage type flexible DC converter module provided by the present invention, wherein the first switch tube T1 and the second switch tube T2 are connected in series to form a first bridge arm, the third switch tube T3 and the fourth switch tube T4 are connected in series to form a second bridge arm, the fifth switch tube T5 and the sixth switch tube T6 are connected in series to form a DC conversion bridge arm, the first bridge arm, the second bridge arm, the capacitor C and the DC conversion bridge arm are connected in parallel, the energy storage inductor L and the energy storage unit E are connected in series to form an energy storage branch, and the energy storage branch is connected in parallel to the sixth switch tube T6.

[0073] Optionally, the output end of the DC conversion upper bridge arm is connected to the input end of the DC conversion lower bridge arm and the first end of the energy storage inductor; the input end of the DC conversion upper bridge arm is connected to the positive DC end of the flexible DC commutation sub-module 101, the second end of the energy storage inductor is respectively connected to the negative DC end of the flexible DC commutation sub-module 101 and the positive pole of the energy storage unit 103, and the output end of the DC conversion lower bridge arm is connected to the negative pole of the energy storage unit 103.

[0074] Among them, when the upper bridge arm of the DC conversion is turned on, the flexible DC commutation submodule 101 is turned on with the energy storage inductor, and the flexible DC commutation submodule 101 charges the energy storage inductor; when the upper bridge arm of the DC conversion is turned off, the flexible DC commutation submodule 101 is disconnected from the energy storage inductor, and the energy storage inductor charges the energy storage unit 103; when the lower bridge arm of the DC conversion is turned on, the flexible DC commutation submodule 101 is disconnected from the energy storage inductor, and the energy storage unit 103 discharges to the energy storage inductor; when the lower bridge arm of the DC conversion is turned off, the flexible DC commutation submodule 101 is turned on with the energy storage inductor, and the energy storage inductor discharges to the flexible DC commutation submodule 101.

[0075] For example, Fig.11 As shown, Fig.11 This is a schematic diagram of another non-isolated bidirectional DC converter provided by the present invention, Figure 2 The half-bridge submodule shown is similar to the above Fig.11 The non-isolated bidirectional DC converter shown in FIG. Fig.12 The energy storage type flexible DC converter module shown in the figure, Fig.12A schematic diagram of another energy storage type flexible DC converter module provided by the present invention, wherein the first switch tube T1 and the second switch tube T2 are connected in series to form a converter bridge arm, the fifth switch tube T5 and the sixth switch tube T6 are connected in series to form a DC conversion bridge arm, the first end of the DC conversion bridge arm is connected to the positive electrode of the capacitor C, the second end of the DC conversion bridge arm is connected to the negative electrode of the energy storage inductor E, the midpoint of the DC conversion bridge arm is connected to the first end of the energy storage inductor L, and the second end of the energy storage inductor L is respectively connected to the positive electrode of the energy storage unit E and the negative electrode of the capacitor C. The energy storage inductor in the DC-DC converter of the type ② energy storage type flexible DC converter module topology serves to directly transitionally store energy: such as Fig.13 As shown, T5 remains off, and when T4 is turned on, the capacitor of the MMC submodule on the flexible DC side discharges energy to the energy storage inductor (i.e., T4=1, T5=0, MMC→energy storage charging); Fig.14 As shown, after T4 is turned off, the energy storage inductor directly charges the energy storage unit (ie, T4 = 0, T5 = 0, MMC → energy storage charging); Fig.15 As shown, when T4 is turned off and T5 is turned on, the energy storage unit stores energy for the inductor (i.e., T4=0, T5=1, energy storage→MMC discharge); Fig.16 As shown, after T5 is turned off, the stored electromagnetic energy is directly converted into electrical energy by the inductor to charge the capacitor of the MMC submodule on the flexible DC side (i.e., T4=0, T5=0, energy storage→MMC discharge).

[0076] For example, by Figure 3 The full bridge submodule shown is the same as the above Fig.11 The non-isolated bidirectional DC converter shown in FIG. Fig.17 The energy storage type flexible DC converter module shown in the figure, Fig.17 A schematic diagram of another energy storage type flexible DC converter module provided by the present invention, wherein the first switch tube T1 and the second switch tube T2 are connected in series to form a first bridge arm, the third switch tube T3 and the fourth switch tube T4 are connected in series to form a second bridge arm, the first bridge arm and the second bridge arm are respectively connected in parallel with the capacitor C, the fifth switch tube T5 and the sixth switch tube T6 are connected in series to form a DC conversion bridge arm, the first end of the DC conversion bridge arm is connected to the positive electrode of the capacitor C, the second end of the DC conversion bridge arm is connected to the negative electrode of the energy storage inductor E, the midpoint of the DC conversion bridge arm is connected to the first end of the energy storage inductor L, and the second end of the energy storage inductor L is respectively connected to the positive electrode of the energy storage unit E and the negative electrode of the capacitor C.

[0077] The energy storage type flexible direct current commutation module proposed in the present invention is composed of three parts: a flexible direct current MMC submodule (i.e., a flexible direct current commutation submodule), a non-isolated bidirectional DC-DC converter, and an energy storage unit. The energy storage unit is connected in parallel to the capacitor side of the flexible direct current submodule via the non-isolated bidirectional DC-DC converter. According to the different energy storage functions of the energy storage inductor, the connection topology of the DC-DC converter and the energy storage unit is as follows: Figure 4 As shown, Fig.11 In addition, the flexible DC MMC submodule can adopt a half-bridge topology or a full-bridge topology. The energy storage flexible DC converter submodule topology proposed by the present invention is obtained as follows: Figure 5 As shown, Fig.10 As shown, Fig.12 As shown and Fig.16 Four types are shown.

[0078] like Figure 4 As shown and Fig.11 The working principles of the two DC-DC converter topologies shown are basically the same. The difference lies in the energy storage process of the energy storage inductor. Taking the half-bridge MMC flexible direct current energy storage commutation module as an example, Figure 6-Figure 9 Explain as Figure 5 The charging and discharging process of the energy storage type flexible DC converter module topology is shown in FIG. Figure 13-Figure 16 Explain as Fig.12 The charging and discharging process of the energy storage type flexible DC converter module topology is shown.

[0079] Embodiment 2:

[0080] The present invention also provides an energy storage type flexible DC converter, which includes multiple parallel bridge arms; the connection points of the multiple bridge arms serve as the DC ends of the converter, and the bridge arms include multiple series-connected energy storage type flexible DC converter modules as described above.

[0081] Among them, the energy storage type flexible DC converter can also be called a flexible DC converter.

[0082] It should be noted that when the flexible DC converter is operating abnormally (i.e.), the MMC is charged or discharged to the energy storage unit by opening and controlling the switches T4 and T5 of the DC-DC converter, thereby maintaining the stability of the capacitor voltage of the flexible DC sub-module: when T5 is turned off and T4 works in PWM control with a constant switching frequency, it is the sub-module energy dissipation mode, that is, when it is detected that the capacitor voltage of the sub-module exceeds the preset value, the MMC charges the energy storage system via the DC-DC, and there is no need to equip a separate energy consumption device to absorb the surplus energy; when T4 is turned off and T5 works in PWM control with a constant switching frequency, it is the energy storage active support mode, that is, after detecting that the capacitor voltage of the sub-module is lower than the threshold, the energy storage is discharged to the MMC via the DC-DC to provide active support.

[0083] The current mainstream technical solution is to support the power grid by configuring active support equipment, but there are generally problems such as poor technical and economic performance, high system complexity, and difficulty in coordination between new equipment. Therefore, it is possible to consider combining energy storage with converters, which can not only use the characteristics of energy storage to increase the inertia of the power system and improve the characteristics of the power grid, but also use converters to improve the flexibility and safety of energy storage access, and also realize the sharing of some components to reduce costs. The present invention proposes an energy storage type flexible direct current converter, which adopts a DC-DC converter to connect a flexible direct current submodule with an energy storage unit to form an energy storage type flexible direct current conversion module. A plurality of energy storage type flexible direct current conversion modules are cascaded to form an energy storage type flexible direct current converter, which can realize the decoupling of the energy storage voltage and the capacitor voltage of the flexible direct current submodule, and control the charging and discharging power of the energy storage by independently controlling the size and direction of the charging and discharging current, so that the energy storage has a strong active supporting ability for deep discharge of the converter. At the same time, the present invention effectively integrates the energy storage with the flexible direct current converter, improves the utilization rate of the energy storage, and the component sharing and modular design improve the economy and flexible reliability of the system. The topology of the energy storage type flexible direct current converter adopts a modular design, which is easy to boost and expand. At the same time, the flexible direct current conversion submodule and the DC-DC converter topology and switching devices are flexible to choose and have a wide applicability.

[0084] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. An energy storage type flexible DC converter module, characterized in that: The energy storage type flexible direct current commutation module comprises: a flexible direct current commutation submodule, a non-isolated bidirectional direct current converter and an energy storage unit; The flexible DC commutation submodule is connected in parallel with the non-isolated bidirectional DC converter; The non-isolated bidirectional DC converter is also connected to the energy storage unit; The non-isolated bidirectional DC converter is used to control the flexible DC commutation submodule to be disconnected from the energy storage unit when the energy storage type flexible DC commutation module is in normal operation, and to control the flexible DC commutation submodule to charge the energy storage unit when the capacitor voltage of the flexible DC commutation submodule is greater than a first preset voltage threshold, and to control the energy storage unit to discharge to the flexible DC commutation submodule when the capacitor voltage of the flexible DC commutation submodule is less than a second preset voltage threshold, so as to maintain the stability of the capacitor voltage of the flexible DC commutation submodule.

2. The energy storage type flexible DC converter module according to claim 1, characterized in that: The non-isolated bidirectional DC converter is also connected to an external controller; The non-isolated bidirectional DC converter is also used to receive different control signals sent by an external controller, and based on the different control signals, adjust the magnitude of the conduction current of the switch tube in the non-isolated bidirectional DC converter to control the magnitude of the charging and discharging current between the flexible DC commutation submodule and the energy storage unit.

3. The energy storage type flexible DC converter module according to claim 1, characterized in that: The flexible DC commutation submodule is a half-bridge submodule, and the half-bridge submodule includes: a first switch tube, a second switch tube and a capacitor; The first switch tube and the second switch tube are connected in series to form a commutation bridge arm, and the commutation bridge arm is connected in parallel with the capacitor.

4. The energy storage type flexible DC converter module according to claim 3, characterized in that: When the first switch tube is turned on and the second switch tube is turned off, the half-bridge sub-module is in a sub-module on-state; when the first switch tube is turned off and the second switch tube is turned on, the half-bridge sub-module is in a sub-module off-state; when the first switch tube and the second switch tube are turned off at the same time, the half-bridge sub-module is in a sub-module locked state.

5. The energy storage type flexible DC converter module according to claim 1, characterized in that: The flexible direct current commutation submodule is a full-bridge submodule, and the full-bridge submodule includes: a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a capacitor; The first switch tube and the second switch tube are connected in series to form a first bridge arm, the third switch tube and the fourth switch tube are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are respectively connected in parallel with the capacitor.

6. The energy storage type flexible DC converter module according to any one of claims 1 to 5, characterized in that: The non-isolated bidirectional DC converter comprises: a DC conversion upper bridge arm, a DC conversion lower bridge arm and an energy storage inductor; The DC conversion upper bridge arm and the DC conversion lower bridge arm are connected in series to form a DC conversion bridge arm; The midpoint of the DC bridge arm is connected to the energy storage inductor; The DC conversion bridge arm is connected to the flexible DC commutation submodule and the energy storage unit respectively, and the energy storage inductor is also connected to the energy storage unit.

7. The energy storage type flexible DC converter module according to claim 6, characterized in that: The output end of the DC conversion upper bridge arm is connected to the input end of the DC conversion lower bridge arm and the first end of the energy storage inductor; The input end of the DC conversion upper bridge arm is connected to the positive DC end of the flexible DC commutation submodule, the second end of the energy storage inductor is connected to the positive pole of the energy storage unit, and the output end of the DC conversion lower bridge arm is respectively connected to the negative DC end of the flexible DC commutation submodule and the negative pole of the energy storage unit.

8. The energy storage type flexible DC converter module according to claim 7, characterized in that: When the upper bridge arm of the DC conversion is turned on, the flexible DC commutation submodule is turned on with the energy storage unit, and the flexible DC commutation submodule charges the energy storage inductor and the energy storage unit; when the upper bridge arm of the DC conversion is turned off, the flexible DC commutation submodule is disconnected with the energy storage unit, and the energy storage inductor charges the energy storage unit; When the lower bridge arm of the DC conversion is turned on, the flexible DC commutation submodule is disconnected from the energy storage unit, and the energy storage unit discharges to the energy storage inductor; when the lower bridge arm of the DC conversion is turned off, the flexible DC commutation submodule is turned on from the energy storage unit, and the energy storage inductor and the energy storage unit discharge to the flexible DC commutation submodule simultaneously.

9. The energy storage type flexible DC converter module according to claim 6, characterized in that: The output end of the DC conversion upper bridge arm is connected to the input end of the DC conversion lower bridge arm and the first end of the energy storage inductor; The input end of the upper bridge arm of the DC conversion is connected to the positive DC end of the flexible DC commutation submodule, the second end of the energy storage inductor is respectively connected to the negative DC end of the flexible DC commutation submodule and the positive pole of the energy storage unit, and the output end of the lower bridge arm of the DC conversion is connected to the negative pole of the energy storage unit.

10. The energy storage type flexible DC converter module according to claim 9, characterized in that: When the upper bridge arm of the DC conversion is turned on, the flexible DC commutation submodule is turned on with the energy storage inductor, and the flexible DC commutation submodule charges the energy storage inductor; when the upper bridge arm of the DC conversion is turned off, the flexible DC commutation submodule is disconnected with the energy storage inductor, and the energy storage inductor charges the energy storage unit; When the bridge arm under the DC conversion is turned on, the flexible DC commutator module is disconnected from the energy storage inductor, and the energy storage unit discharges to the energy storage inductor; when the bridge arm under the DC conversion is turned off, the flexible DC commutator module is turned on from the energy storage inductor, and the energy storage inductor discharges to the flexible DC commutator module.

11. An energy storage type flexible DC converter, characterized in that: The energy storage type flexible DC converter comprises a plurality of bridge arms connected in parallel; the connection point of the plurality of bridge arms serves as the DC end of the converter, and the bridge arms comprise a plurality of energy storage type flexible DC converter modules as described in any one of claims 1 to 10 connected in series.

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