A kind of energy storage converter, control method of balancing circuit and energy storage system

Abstract

The application provides a kind of energy storage converter, the control method of balancing circuit and energy storage system.The energy storage converter includes DC / DC conversion circuit, balancing circuit, split capacitor, DC / AC conversion circuit and controller.The energy storage converter reuses the partial switch device of DC / DC conversion circuit and flying capacitor, when the midpoint potential of split capacitor is unbalanced, control first power device and second power device in balancing circuit respectively with fourth switch and first switch in DC / DC conversion circuit cooperate with each other, make flying capacitor in DC / DC conversion circuit and positive bus capacitor or negative bus capacitor in split capacitor form current loop, and then stabilize the midpoint potential of split capacitor.The topology of balancing circuit is simple, the number of power device used is less, the cost is low, and the voltage stress of power device is small, the inductance value of filter inductance in balancing circuit is small, and the working efficiency of balancing circuit is obviously improved.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to an energy storage converter, a control method for a balancing circuit, and an energy storage system. Background Technology

[0002] Neutral point clamped (NPC) three-level DC / AC converter circuits are increasingly used in medium- and high-voltage power conversion systems (PCS) due to their advantages such as large output capacity, high output voltage, and low current harmonic content. For a two-stage PCS, the DC source can be coupled to the DC bus via the PCS's DC / DC converter circuit. Then, the DC is converted to AC by a cascaded NPC three-level DC / AC converter circuit. The AC is then passed through an LCL filter to eliminate harmonic currents before being delivered to the grid or load.

[0003] In off-grid or grid-connected industrial and commercial microgrids, PCS (Power Control System) typically employs grid-based control, exhibiting voltage source characteristics to enhance power system stability. However, facing complex and variable load conditions, PCS must be capable of handling unbalanced loads, harmonic loads, and half-wave rectified loads. This necessitates that PCS possess neutral point potential balancing capabilities.

[0004] However, both NPC three-level and NPC multi-level DC / AC converter circuits generally suffer from DC-side midpoint potential fluctuations, leading to severe distortion of the output voltage waveform, increased harmonic losses, and limited application scenarios for the PCS. To address this issue, the industry typically employs software algorithm modulation and the addition of hardware balancing circuits. However, the balancing capability of software algorithm modulation is constrained by small vector duty cycles. Under high modulation ratio conditions, this method has limited control over the DC-side midpoint potential balance, making it difficult for the corresponding PCS to meet the requirements of complex load conditions. In contrast, hardware balancing circuits are generally more stable than software algorithm modulation. Therefore, proposing a stable, effective, and cost-efficient balancing circuit is crucial. Summary of the Invention

[0005] This application provides an energy storage converter and its control method, as well as an energy storage system, to solve the problem of DC side midpoint potential drift in NPC three-level DC / AC converter circuits.

[0006] In a first aspect, embodiments of this application provide an energy storage converter capable of bidirectional conversion of current from DC to AC and from AC to DC. Specifically, the energy storage converter includes: a DC / DC conversion circuit, a balancing circuit, a split capacitor, and a DC / AC conversion circuit.

[0007] The DC / DC converter circuit is connected to the DC source and the positive and negative DC buses. The balancing circuit is connected to the DC / DC converter circuit and the midpoint of the split capacitor. The split capacitor is connected in parallel with the positive and negative DC buses. The DC side of the DC / AC converter circuit is connected to the midpoint of the split capacitor and the positive and negative DC buses. The AC side of the DC / AC converter circuit is connected to the power grid or load.

[0008] The DC / DC converter circuit includes a flying capacitor and a first switch, a second switch, a third switch, and a fourth switch connected in series. The first switch is connected to the positive DC bus, and the fourth switch is connected to the negative DC bus. The series connection point of the first and second switches is connected to the series connection point of the third and fourth switches via the flying capacitor. Furthermore, it is worth noting that for an N-level DC / DC converter circuit, if the duty cycles of all switches are equal, the voltage across the flying capacitor can be essentially stable at k / N (k = 1, 2, ..., N-1). Therefore, for example, in the DC / DC converter circuit of this application, the voltage across the flying capacitor can be essentially stable at half the bus voltage, i.e., 1 / 2 Udc.

[0009] A split capacitor consists of a positive bus capacitor and a negative bus capacitor connected in series. The positive and negative bus capacitors have the same capacitance value. The split capacitor is connected in parallel with the positive and negative DC buses. The positive bus capacitor is connected to the midpoint of the split capacitor and the positive DC bus, while the negative bus capacitor is connected to the midpoint of the split capacitor and the negative DC bus.

[0010] The balancing circuit includes: a first power device, a second power device, and a filter inductor.

[0011] The balancing circuit is used to form a current loop between the flying capacitor and the positive bus capacitor or the negative bus capacitor, so as to reduce the difference between the positive bus capacitor voltage or the negative bus capacitor voltage and 1 / 2Udc, and the potential at the midpoint of the split capacitor tends to be balanced.

[0012] According to one embodiment, the balancing circuit includes three terminals, wherein the first terminal is connected to the midpoint of the split capacitor, and the second and third terminals are both connected to the DC / DC converter circuit. By connecting the balancing circuit to the DC / DC converter circuit and the midpoint of the balancing bridge arm, the voltage stress borne by the first and second power devices in the balancing circuit can be greatly reduced, extending the service life of the power devices and reducing hardware costs.

[0013] According to one embodiment, one end of the first power device is connected to one end of the second power device. The other end of the first power device is the second terminal of the above embodiment, connected to the positive terminal of the flying capacitor. The other end of the second power device is the third terminal of the above embodiment, connected to the negative terminal of the flying capacitor. The series connection point of the first power device and the second power device is connected to one end of the filter inductor. The other end of the filter inductor is the first terminal of the above embodiment, connected to the midpoint of the split capacitor. The balancing circuit has a simple structure, requires fewer components, and has low hardware cost.

[0014] According to one embodiment, both the first power device and the second power device are fully controllable devices, and the energy storage converter also includes a controller. The fully controllable device includes a switching transistor and a diode connected in antiparallel to it, such as an Insulated Gate Bipolar Transistor (IGBT) or a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). The controller is used to control both the second power device and the first switch to be turned on, so that a current loop is formed between the first switch, the flying capacitor, the second power device, and the positive bus capacitor, reducing the difference between the positive bus capacitor voltage and 1 / 2Udc. Alternatively, the controller is used to control both the first power device and the fourth switch to be turned on, so that a current loop is formed between the fourth switch, the flying capacitor, the first power device, and the negative bus capacitor, reducing the difference between the negative bus capacitor voltage and 1 / 2Udc.

[0015] When both the first and second power devices are fully controllable devices, the power devices in the balancing circuit can flexibly change according to the states of the first and fourth switches in the DC / DC converter circuit. At the same time, since the fully controllable devices can achieve bidirectional conduction, regardless of whether the positive or negative bus capacitor voltage is higher or lower than 1 / 2Udc, the flying capacitor can charge and discharge the positive or negative bus capacitor in a timely manner according to the switch state at that moment, thereby increasing or decreasing the positive or negative bus capacitor voltage, thus stabilizing the positive or negative bus capacitor voltage. It has a strong ability to control the midpoint potential of the split capacitor.

[0016] According to one embodiment, both the first power device and the second power device are diodes, and the first power device and the second power device are connected in reverse series, that is, the anode of the first power device is connected to the cathode of the second power device, or the cathode of the first power device is connected to the anode of the second power device.

[0017] By connecting the first power device and the second power device in reverse series, only one power device in the balancing circuit can be turned on when the first switch or the fourth switch is turned on. This ensures that under different switching states, only one of the positive bus capacitor or the negative bus capacitor can form a current loop with the flying capacitor, thereby achieving the effect of precisely adjusting the voltage of the positive bus capacitor or the negative bus capacitor.

[0018] Specifically, when both the first and second power devices are diodes, although the balancing circuit can also regulate the voltages of the positive and negative bus capacitors, since diodes can only achieve single-phase conduction, a current loop can only be formed between the first switch, the flying capacitor, the second power device, and the positive bus capacitor when the positive bus capacitor voltage is greater than the flying capacitor voltage. This allows the positive bus capacitor to charge the flying capacitor, causing its voltage to drop closer to 1 / 2 Udc, and the midpoint potential of the split capacitor to tend towards equilibrium. Similarly, in the balancing circuit, the first power device can only form a current loop between the fourth switch, the flying capacitor, the first power device, and the negative bus capacitor when the negative bus capacitor voltage is greater than the flying capacitor voltage. This allows a current loop to be formed between the negative bus capacitor and the flying capacitor, causing the negative bus capacitor to charge the flying capacitor, causing its voltage to drop closer to 1 / 2 Udc, and the midpoint potential of the split capacitor to tend towards equilibrium.

[0019] It should be noted that the aforementioned situation, where the positive or negative bus capacitor forms a current loop with the flying capacitor in the DC / DC converter circuit, and the positive or negative bus capacitor charges the flying capacitor, applies to the following balancing circuit: the cathode of the first power device is connected to the positive terminal of the flying capacitor, the anode is connected to the cathode of the second power device, and the anode of the second power device is connected to the negative terminal of the flying capacitor. Understandably, when the cathode and anode positions of the first and second power devices are interchanged, the positive or negative bus capacitor can only form a current loop with the flying capacitor when its voltage is lower than the flying capacitor's voltage. This allows the flying capacitor to charge the positive or negative bus capacitor, increasing its voltage and causing the midpoint potential of the split capacitor to tend towards equilibrium. In summary, when both the first and second power devices in the balancing circuit are diodes, the control over the midpoint potential is weaker, but its economic efficiency is superior.

[0020] According to one embodiment, one of the first power device and the second power device is a fully controlled device, and the other is a diode. The energy storage converter also includes a controller. When the first power device is a fully controlled device and the second power device is a diode, the controller controls both the first power device and the fourth switch to be turned on, so that the fourth switch, the first power device, the flying capacitor, and the negative bus capacitor form a current loop, thereby reducing the difference between the negative bus capacitor voltage and 1 / 2Udc. When the first power device is a diode and the second power device is a fully controlled device, the controller controls both the second power device and the first switch to be turned on, so that the first switch, the second power device, the flying capacitor, and the positive bus capacitor form a current loop, thereby reducing the difference between the positive bus capacitor voltage and 1 / 2Udc. When one of the first power device and the second power device in the balancing circuit is a fully controlled device and the other is a semi-controlled device, its control capability for the midpoint potential and its economy are both better.

[0021] According to one embodiment, the balancing circuit includes three terminals: a first terminal connected to the midpoint of a split capacitor, a second terminal connected to the positive or negative terminal of a flying capacitor, and a third terminal connected to the positive or negative DC bus. By connecting the balancing circuit to the DC / DC converter circuit, the midpoint of the balancing bridge arm, and the positive / negative DC bus, the voltage stress on the first and second power devices in the balancing circuit can be reduced, extending the lifespan of the power devices and reducing hardware costs.

[0022] According to one embodiment, one end of the first power device, one end of the second power device, and one end of the filter inductor are connected to a single point. The other end of the power device, which is a diode, is the third terminal in the above embodiment and is connected to the positive or negative DC bus. The other end of the power device, which is a fully controllable device, is the first or second terminal in the above embodiment and is connected to the midpoint of the split capacitor or the positive or negative terminal of the flying capacitor. In the balancing circuit, one of the first power device and the other of the second power device is a diode and the other is a fully controllable device. With this configuration, the balancing circuit has good balancing capability for the midpoint potential of the split capacitor and is also economical.

[0023] According to one embodiment, the first power device is a fully controlled device, the second power device is a diode, and the energy storage converter also includes a controller. The controller is used to control the first power device and the fourth switch to be turned on, so that a current loop is formed between the fourth switch, the flying capacitor, the first power device, and the negative bus capacitor, and the difference between the voltage of the negative bus capacitor and half of the DC bus voltage is reduced, and the second power device plays a freewheeling role.

[0024] According to one embodiment, the first power device is a diode, the second power device is a fully controlled device, and the energy storage converter also includes a controller. The controller is used to control the second power device and the first switch to be turned on, so that a current loop is formed between the first switch, the flying capacitor, the second power device, and the positive bus capacitor. The difference between the voltage of the positive bus capacitor and half of the DC bus voltage is reduced, and the first power device plays a freewheeling role.

[0025] According to one embodiment, the energy storage converter further includes a controller. A switch is provided on the connection line between the balancing circuit and the midpoint of the split capacitor. The switch includes a mechanical switch, an active semiconductor switch, or a passive semiconductor switch. When the positive bus capacitor voltage or the negative bus capacitor voltage is the same as 1 / 2Udc, the controller controls the switch to open to reduce the loss of the balancing circuit. When the positive bus capacitor voltage or the negative bus capacitor voltage is different from 1 / 2Udc, the controller controls the switch to close to balance the potential at the midpoint of the split capacitor.

[0026] According to one embodiment, the topology of the bridge arm in the DC / AC conversion circuit can be: a three-level topology such as an I-type NPC, ANPC, or T-type NPC that requires midpoint clamping, or other multi-level topologies. This application does not limit this.

[0027] Secondly, embodiments of this application provide an energy storage system, which includes an energy storage converter and an energy storage battery as described in any of the first aspects. The energy storage battery is connected to the DC / DC conversion circuit in the energy storage converter. The energy storage converter is used to realize bidirectional conversion between AC and DC power, converting DC power from the energy storage battery or renewable energy power generation equipment into AC power and transmitting the AC power to the power grid or load, or converting AC power from the power grid into DC power to charge the energy storage battery. The renewable energy power generation equipment can be a photovoltaic module, or it can be a hydroelectric or wind power generation module.

[0028] The energy storage battery can be a chemical energy storage element such as a lead-acid battery or a lithium battery, or an electromagnetic energy storage element such as a supercapacitor; this application does not impose any restrictions on this.

[0029] Thirdly, embodiments of this application provide a control method for a balancing circuit. The method includes: controlling the on and off states of a first power device and a second power device in the balancing circuit and a first switch, a second switch, a third switch, and a fourth switch in the DC / DC conversion circuit, so that a current loop is formed between the flying capacitor and the positive bus capacitor or the negative bus capacitor in the DC / DC conversion circuit, and the difference between the positive bus capacitor voltage or the negative bus capacitor voltage and half of the bus voltage is reduced.

[0030] According to one embodiment, the method includes: controlling both a first power device and a fourth switch to be turned on, so that a current loop is formed between the fourth switch, the flying capacitor, the first power device, and the negative bus capacitor, thereby reducing the difference between the voltage of the negative bus capacitor and half of the DC bus voltage.

[0031] According to one embodiment, the method includes: controlling both the second power device and the first switch to be turned on, so that a current loop is formed between the first switch, the flying capacitor, the second power device, and the positive bus capacitor, and the difference between the positive bus capacitor voltage and half of the DC bus voltage is reduced.

[0032] According to one embodiment, a switch is provided between the balancing circuit and the connection point of the positive bus capacitor and the negative bus capacitor. The method includes: controlling the switch to close in response to the positive bus capacitor voltage or the negative bus capacitor voltage being unequal to half of the DC bus voltage; and controlling the switch to open in response to the positive bus capacitor voltage or the negative bus capacitor voltage being equal to half of the DC bus voltage.

[0033] This application fully utilizes the characteristic that the voltage of the flying capacitor can be basically stabilized at 1 / 2Udc. When the first power device and the second power device are not both diodes, the first power device and the fourth switch have the same on and off states, so that the flying capacitor charges and discharges the negative bus capacitor, and the potential at the midpoint of the split capacitor tends to be balanced. Alternatively, in the balancing circuit, the second power device and the first switch have the same on and off states, so that the flying capacitor charges and discharges the positive bus capacitor, and the potential at the midpoint of the split capacitor tends to be balanced.

[0034] Among them, the balancing circuit has a simple topology, fewer power devices, better economic efficiency, and significantly reduced voltage stress on the power devices, thus greatly improving the operating stability of the balancing circuit. When all power devices in the balancing circuit are diodes, the two diodes are connected in reverse series. This ensures that when the first or fourth switch in the DC / DC converter circuit is turned on, only one power device in the balancing circuit is synchronously turned on. This allows only one of the positive or negative bus capacitors to form a current loop with the flying capacitor of the DC / DC converter circuit under the corresponding switching state, achieving precise adjustment of the positive or negative bus capacitor voltage. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the DC-coupled architecture and AC-coupled architecture of an energy storage system;

[0036] Figure 2 This is a schematic diagram of a common two-stage three-level energy storage converter topology.

[0037] Figure 3This is a schematic diagram of the additional balancing circuit topology for two common NPC three-level DC / AC converter circuits;

[0038] Figure 4 A topology diagram of a two-stage three-level energy storage converter with an additional balancing circuit provided in this application;

[0039] Figure 5 A schematic diagram of the circuit topology of a DC / DC converter circuit provided in this application;

[0040] Figure 6 A topology diagram of a two-stage three-level energy storage converter with an additional balancing circuit provided in this application;

[0041] Figure 7 A schematic diagram of the topology of a two-stage three-level converter circuit with an additional balanced circuit provided in this application;

[0042] Figure 8 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0043] Figure 9 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0044] Figure 10 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0045] Figure 11 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0046] Figure 12 A schematic diagram of the topology of a two-stage three-level converter circuit with an additional balanced circuit provided in this application;

[0047] Figure 13 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0048] Figure 14 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0049] Figure 15 A schematic diagram of the topology of a two-stage three-level converter circuit with an additional balanced circuit provided in this application;

[0050] Figure 16 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0051] Figure 17 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0052] Figure 18 A topology diagram of a two-stage three-level energy storage converter with an additional balancing circuit provided in this application;

[0053] Figure 19 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0054] Figure 20 A schematic diagram of the switching conduction state of a DC / DC converter circuit and a balancing circuit provided in this application;

[0055] Figure 21 Schematic diagrams of several gating switches provided in this application;

[0056] Figure 22 Several three-level topologies are provided in this application;

[0057] Figure 23 A schematic diagram of the topology of the DC-coupled architecture provided in this application;

[0058] Figure 24 A schematic diagram of the topology of the DC-coupled architecture for the additional balancing circuit provided in this application;

[0059] Figure 25 A schematic diagram of the topology of the DC / DC converter circuit for the additional controller provided in this application;

[0060] Figure 26 A schematic diagram of a control method for a balanced circuit provided in this application;

[0061] Figure 27 A schematic diagram of a control method for a balanced circuit provided in this application; Detailed Implementation

[0062] PCS, also known as a bidirectional energy storage inverter or energy storage converter, is typically installed between energy storage batteries and the power grid (or load) to achieve bidirectional energy conversion. Specifically, Figure 1The diagram illustrates the DC-coupled and AC-coupled architectures of a photovoltaic-storage system. In the DC-coupled architecture, the energy storage battery and photovoltaic modules couple DC power to the combiner cabinet (DC bus). The power generation system (PCS) further converts the DC power to AC power and supplies it to the grid or AC loads. In the AC-coupled architecture, the PCS converts the DC power from the energy storage battery to AC power and then supplies it to the grid or directly to loads via the AC bus. When the energy storage battery is charging, both the DC-coupled and AC-coupled architectures allow the PCS to convert AC power from the grid back to DC power and feed it back to the energy storage battery. The energy storage battery can be a chemical energy storage element such as a lead-acid battery or lithium battery, or an electromagnetic energy storage element such as a supercapacitor.

[0063] Based on the number of power conversion stages, power generation systems (PCS) can be divided into single-stage and two-stage structures. A single-stage PCS includes a single-stage bidirectional DC / AC converter circuit, while a two-stage PCS includes a front-stage DC / DC converter circuit and a rear-stage DC / AC converter circuit. The two-stage PCS, through the configuration of the front-stage DC / DC converter circuit, can adjust the DC-side voltage, thereby expanding the voltage range applicable to the energy storage battery. Based on the number of output levels, PCS can be divided into two-level, three-level, and multi-level structures. Among these, three-level and multi-level structures offer higher output waveform quality, lower switching transistor voltage stress, and lower electromagnetic interference, making them better suited to the development trend of high-voltage, high-capacity new energy power generation.

[0064] In both off-grid and grid-connected microgrid scenarios, the power generation system (PCS) is a core component. This is because both photovoltaic (PV) power generation and loads are volatile, and PV modules can only generate electricity, not absorb it. If the system only contains PV power generation equipment, the system operation may be unbalanced. When the power of renewable energy exceeds the load power, the system may fail. The PCS, however, can both absorb and generate energy, and its rapid response allows it to play a balancing role in the system. Therefore, as mentioned in the background section, the PCS needs to be able to handle unbalanced loads, harmonic loads, and half-wave rectified loads under complex and variable load conditions. This places high demands on the DC-side midpoint voltage balancing capability of the DC / AC conversion circuit within the PCS.

[0065] However, three-level or multi-level DC / AC converter circuits suffer from DC-side midpoint potential fluctuations. These fluctuations can cause distortion of the DC / AC converter output waveform, inconsistent voltage stress on the switches, shorten the lifespan of the switches, and even prevent the PCS from functioning properly. Therefore, it is of great significance to study the balancing strategy of the DC-side midpoint potential in three-level or multi-level DC / AC converter circuits.

[0066] It should be noted that this application uses the NPC three-level DC / AC converter circuit as an example for discussion. In practical applications, the NPC DC / AC converter circuit can also be expanded to other NPC multi-level DC / AC converter circuits. No specific limitation is made here, and the choice can be made according to the specific situation. All of these are within the protection scope of this application.

[0067] Currently, the industry typically uses the method of setting up a balancing circuit to solve the problem of DC side midpoint potential fluctuation in NPC three-level DC / AC converter circuits. Figure 2 The diagram shows a typical two-stage PCS topology with an additional balancing circuit. The PCS includes a DC / DC converter circuit, a balancing circuit, split capacitors, a DC / AC converter circuit, and an LCL filter. The split capacitors are connected in parallel between the positive and negative DC buses, including a positive bus capacitor Cp and a negative bus capacitor Cn connected in series. The series connection point O is the midpoint of the DC side of the DC / AC converter circuit; for ease of description, this application refers to it as the midpoint O of the split capacitors. The balancing circuit is located between the DC / DC converter circuit and the DC / AC converter circuit and is directly connected in parallel with the positive and negative DC buses.

[0068] Specifically, Figure 3 Figure (a) shows a balanced circuit that is directly connected in parallel with the positive and negative DC buses. It consists of three components (two switching transistors T1 and T2, and an inductor L1), and is relatively inexpensive and compact, making it widely applicable. However, the two switching transistors T1 and T2 in this balanced circuit need to operate at complementary high frequencies, and the switching transistors experience significant voltage stress, resulting in substantial switching losses during operation. In contrast, Figure 3 Figure (b) shows another type of balancing circuit, which consists of a time-division multiplexing BUCK circuit and a BOOST circuit. Since the BOOST circuit is not operating when the BUCK circuit is operating, and vice versa, only one switching transistor (T1 or T2) is turned on at high frequency each time the circuit operates, resulting in relatively low switching losses. However, this additional balancing circuit requires a total of eight components: two switching transistors, two capacitors, two inductors, and two diodes, leading to higher cost and size, and limiting its application range.

[0069] The following will combine Figures 4 to 27 This application provides examples and explanations of the energy storage converter and its control method, as well as the working principle of the energy storage system.

[0070] First, see Figure 4 , Figure 4This is a circuit topology diagram of an energy storage converter 10 provided in this application. The energy storage converter 10 includes a DC / DC converter circuit 11, a balancing circuit 12, a split capacitor, a three-level DC / AC converter circuit 13, and an LCL filter 14. The balancing circuit 12 includes three terminals: a first terminal, a second terminal, and a third terminal.

[0071] Specifically, such as Figure 4 As shown in (a), the first terminal is connected to the midpoint O of the split capacitor, and the second and third terminals are both connected to the DC / DC converter circuit 11, or, as shown in (a). Figure 4 As shown in (b) and (c), the first terminal is connected to the midpoint O of the split capacitor, the second terminal is connected to the DC / DC converter circuit 11, and the third terminal is connected to the positive DC bus or the negative DC bus.

[0072] and Figure 2 The energy storage converter structure shown differs from the one provided in this application. In the energy storage converter 10, the balancing circuit 12 is connected to the DC / DC conversion circuit 11 and the midpoint O of the split capacitor, instead of being directly connected in parallel between the positive and negative DC buses. It is understood that... Figure 3 The balancing circuit 12 shown in (a) is directly connected in parallel to the positive and negative DC buses. When one of the switching transistors (such as T1) is turned on, the voltage across the other switching transistor (such as T2) is the DC bus voltage, i.e., Udc. In contrast, the balancing circuit 12 of this application is connected to the DC / DC converter circuit 11 and the midpoint O of the split capacitor. The voltage stress on the balancing circuit 12 is reduced, which helps to extend the service life of the balancing circuit 12 and reduce hardware costs.

[0073] When the DC source (energy storage battery or photovoltaic module) is in a discharging state, the working principle of the energy storage converter 10 is as follows: the DC / DC conversion circuit 11 boosts the low-voltage DC power from the DC source and couples it to the DC bus. Then, the current is transmitted through the DC bus and the balancing circuit 12 to the three-level DC / AC conversion circuit 13 and converted into AC power. The AC power continues to pass through the LCL filter 14 to reduce ripple current, and finally the AC power is delivered to the grid or load.

[0074] See Figure 5 , Figure 5 yes Figure 4 A schematic diagram of the circuit topology of the DC / DC converter circuit 11. The DC / DC converter circuit 11 includes a flying capacitor C. flyThe system comprises four switches connected in series: a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4. Each switch includes a switching transistor and diodes connected in antiparallel, namely D1, D2, D3, and D4. Specifically, the first switch Q1 is connected to the positive DC bus, and the fourth switch Q4 is connected to the negative DC bus. The series connection point of the first switch Q1 and the second switch Q2 is connected through a flying capacitor C. fly The connection point that connects the third switch Q3 and the fourth switch Q4 in series.

[0075] The aforementioned first switch Q1, second switch Q2, third switch Q3, or fourth switch Q4 can be MOSFETs, IGBTs, or other controllable switching devices made of silicon semiconductor material (Si), or third-generation wide-bandgap semiconductor material silicon carbide (SiC), or gallium nitride (GaN), or diamond, or zinc oxide (ZnO), or other materials. It should also be noted that the first switch Q1 and the second switch Q2, the third switch Q3, and the fourth switch Q4 operate alternately, with their drive signals differing by 180°. The first switch Q1 and the fourth switch Q4, and the second switch Q2 and the third switch Q3, are complementary in conduction; that is, the first switch Q1 and the fourth switch Q4 do not conduct simultaneously, and the second switch Q2 and the third switch Q3 do not conduct simultaneously. (Flying capacitor C) fly The voltage across the two ends can be basically stabilized at 1 / 2Udc.

[0076] See Figure 6 , Figure 6 yes Figure 4 The diagram shows the topology of the energy storage converter 10 corresponding to (a), wherein the balancing circuit 12 includes a first power device, a second power device, and a filter inductor. Specifically, one end of the first power device and one end of the second power device are connected in the balancing circuit 12, and the other end of the first power device is connected to the flying capacitor C. fly The positive terminal of the second power device is connected to the other end of the flying capacitor C. fly The negative terminals are connected, and the series connection point of the first and second power devices is connected to one end of the filter inductor. The other end of the filter inductor is connected to the midpoint O of the split capacitor. Based on the specific device types of the two power devices in the balanced circuit 12, it can include, for example... Figure 6 There are four implementation methods: (a), (b), (c), and (d).

[0077] like Figure 6 As shown in (a), both the first power device Q5 and the second power device Q6 in the balanced circuit 12 are fully controllable devices. Figure 6As shown in (b), in the balanced circuit 12, the first power device Q5 is a fully controllable device, and the second power device D6 is a diode. Figure 6 As shown in (c), in the balanced circuit 12, the first power device D5 is a diode, and the second power device Q6 is a fully controllable device. Figure 6 As shown in (d), in the balancing circuit 12, the first power device D5 and the second power device D6 are both diodes. The first power device D5 and the second power device D6 are connected in reverse series, that is, the anode of the first power device D5 is connected to the cathode of the second power device D6, or the cathode of the first power device D5 is connected to the anode of the second power device D6.

[0078] The following explanation will illustrate the operating principle of the balancing circuit 12, assuming the DC source is in discharge mode and both the first power device Q5 and the second power device Q6 are fully controllable devices. (See also...) Figure 7 , Figure 7 for Figure 6 The diagram shows the topology of the energy storage converter 10 corresponding to (a). The topology has been drawn differently for easier understanding, but the topology itself remains unchanged.

[0079] See Figure 8 , Figure 8 In Figure (a), when the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5, the waveforms representing the on or off states of the four switches and the two power devices in the balancing circuit of the DC / DC converter circuit 11 are shown. Figure 8 (b) is Figure 7 The topology diagram shows the corresponding switching states of the DC / DC converter circuit 11 and the balancing circuit 12 during the time periods T0-T1 and T2-T3. Specifically, during the time periods T0-T1 and T2-T3, the first switch Q1, the second switch Q2, and the second power device Q6 are turned on, while the third switch Q3, the fourth switch Q4, and the first power device Q5 are turned off. The DC power supplied by the DC source is coupled to the positive DC bus through the first switch Q1 and the second switch Q2. At this time, if the DC bus is in an unbalanced state, that is, the voltage of the positive bus capacitor Cp or the negative bus capacitor Cn is not equal to 1 / 2Udc, the conduction of the first switch Q1 and the second power device Q6 will cause the flying capacitor C... fly A current loop is formed between the capacitor and the positive bus capacitor Cp, thereby utilizing the flying capacitor C fly The voltage can be basically stabilized at 1 / 2Udc, and the flying capacitor C fly By charging and discharging the positive bus capacitor Cp, the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc is reduced, and the voltage at the midpoint O of the split capacitor tends to be balanced.

[0080] Specifically, when the voltage across the positive bus capacitor Cp is greater than that across the flying capacitor C... flyWhen the voltage is applied, the positive bus capacitance Cp is equal to the flying capacitance C. fly Charging occurs via the first switch Q1, the second power device Q6, and the flying capacitor C. fly In the circuit formed by the positive bus capacitor Cp and the filter inductor L, the current flows from the connection point of the third switch Q3 and the fourth switch Q4 to the midpoint O of the split capacitor. That is, the current flows into the midpoint O of the split capacitor (in the same direction as the current flow on the DC bus when the DC source is in a discharging state). The voltage of the positive bus capacitor Cp decreases, the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc decreases, and the potential of the midpoint O of the split capacitor tends to be balanced.

[0081] Similarly, when the voltage across the positive bus capacitor Cp is less than that across the flying capacitor C... fly When the voltage is applied, the flying capacitor C fly Charging the positive bus capacitor Cp, through the first switch Q1, the second power device Q6, and the flying capacitor C fly In the circuit formed by the positive bus capacitor Cp and the filter inductor L, the current flows from the midpoint O of the split capacitor to the connection point of the third switch Q3 and the fourth switch Q4, that is, the current flows out of the midpoint O of the split capacitor (opposite to the direction of current flow on the DC bus when the DC source is in a discharging state). The voltage of the positive bus capacitor Cp increases, the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc decreases, and the potential of the midpoint O of the split capacitor tends to be balanced.

[0082] See Figure 9 , Figure 9 In Figure (a), when the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5, the waveforms representing the on or off states of the four switches and the two power devices in the balancing circuit of the DC / DC converter circuit 11 are shown. Figure 9 (b) is Figure 7 The diagram shows the topology of the DC / DC converter circuit 11 and the balancing circuit 12 during the T1-T2 period, corresponding to their switching states. Specifically, during the T1-T2 period, the first switch Q1, the third switch Q3, and the second power device Q6 are turned on, while the second switch Q2, the fourth switch Q4, and the first power device Q5 are turned off. The DC power supplied by the DC source is coupled to the positive DC bus through the third switch Q3 and the first switch Q1. At this time, if the DC bus is in an unbalanced state, i.e., the voltage across the positive bus capacitor Cp is not equal to 1 / 2Udc, the conduction of the first switch Q1 and the second power device Q6 will cause the flying capacitor C... fly A current loop is formed between the capacitor and the positive bus capacitor Cp, thereby utilizing the flying capacitor C fly The voltage can be stabilized at 1 / 2Udc, and the flying capacitor C fly By charging and discharging the positive bus capacitor Cp, the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc is reduced, and the potential at the midpoint O of the split capacitor tends to be balanced.

[0083] Specifically, when the voltage across the positive bus capacitor Cp is greater than that across the flying capacitor C... fly When the voltage is applied, the positive bus capacitance Cp flows towards the flying capacitor C. fly Charging occurs via the first switch Q1, the second power device Q6, and the flying capacitor C. fly In the circuit formed by the positive bus capacitor Cp and the filter inductor L, the current flows from the connection point of the third switch Q3 and the fourth switch Q4 to the midpoint O of the split capacitor. That is, the current flows into the midpoint O of the split capacitor, the voltage of the positive bus capacitor Cp decreases, the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc decreases, and the voltage at the midpoint O of the split capacitor tends to be balanced.

[0084] Similarly, when the voltage across the positive bus capacitor Cp is less than that across the flying capacitor C... fly When the voltage is applied, the flying capacitor C fly Charging the positive bus capacitor Cp, through the first switch Q1, the second power device Q6, and the flying capacitor C fly In the circuit formed by the positive bus capacitor Cp and the filter inductor L, the current flows from the midpoint O of the split capacitor to the connection point of the third switch Q3 and the fourth switch Q4, that is, the current flows out of the midpoint O of the split capacitor, which increases the voltage of the positive bus capacitor Cp, reduces the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, and the potential of the midpoint O of the split capacitor tends to be balanced.

[0085] See Figure 10 , Figure 10 In Figure (a), when the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5, the waveforms representing the on or off states of the four switches and the two power devices in the balancing circuit of the DC / DC converter circuit 11 are shown. Figure 10 (b) is Figure 7 The diagram shows the topology of the DC / DC converter circuit 11 and the balancing circuit 12 during the T3-T4 period, corresponding to their switching states. Specifically, during the T3-T4 period, the second switch Q2, the fourth switch Q4, and the first power device Q5 are turned on, while the first switch Q1, the third switch Q3, and the second power device Q6 are turned off. The DC power supplied by the DC source is coupled to the negative DC bus through the second switch Q2 and the fourth switch Q4. At this time, if the DC bus is in an unbalanced state, i.e., the voltage of the positive bus capacitor Cp or the negative bus capacitor Cn is not equal to 1 / 2Udc, the conduction of the fourth switch Q4 and the first power device Q5 will cause the flying capacitor C... fly A current loop is formed between the capacitor and the negative bus capacitor Cn, thereby utilizing the flying capacitor C fly The voltage can be basically stabilized at 1 / 2Udc, and the flying capacitor C flyBy charging and discharging the negative bus capacitor Cn, the absolute value of the difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc decreases, and the potential at the midpoint O of the split capacitor tends to be balanced.

[0086] Specifically, when the voltage across the negative bus capacitor Cn is greater than that across the flying capacitor C fly When the voltage is applied, the negative bus capacitor Cn flows towards the flying capacitor C. fly Charging occurs at the fourth switch Q4, the first power device Q5, and the flying capacitor C. fly In the circuit formed by the negative bus capacitor Cn and the filter inductor L, the current flows from the midpoint O of the split capacitor to the connection point of the first switch Q1 and the second switch Q2. That is, the current flows out of the midpoint O of the split capacitor, which reduces the voltage of the negative bus capacitor Cn, reduces the absolute value of the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, and the potential of the midpoint O of the split capacitor tends to be balanced.

[0087] Similarly, when the voltage across the negative bus capacitor Cn is less than that across the flying capacitor C fly When the voltage is applied, the flying capacitor C fly As the negative bus capacitor Cn is charged, in the circuit formed by the fourth switch Q4, the first power device Q5, the flying capacitor Cfly, the negative bus capacitor Cn, and the filter inductor L, the current flows from the connection point of the first switch Q1 and the second switch Q2 to the midpoint O of the split capacitor. That is, the current flows into the midpoint O of the split capacitor, which increases the voltage of the negative bus capacitor Cn, reduces the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, and the potential of the midpoint O of the split capacitor tends to be balanced.

[0088] See Figure 11 , Figure 8 In Figure (a), when the duty cycle D of the DC / DC converter circuit 11 is less than 0.5, the waveforms representing the on or off states of the four switches and the two power devices in the balancing circuit of the DC / DC converter circuit 11 are shown. Figure 11 (b) is Figure 7 The topology diagram shows the corresponding switching states of the DC / DC converter circuit 11 and the balancing circuit 12 during the time periods T0-T1 and T2-T3. Specifically, during the time periods T0-T1 and T2-T3, the third switch Q3, the fourth switch Q4, and the first power device Q5 are turned on, while the first switch Q1, the second switch Q2, and the second power device Q6 are turned off. The DC power supplied by the DC source is coupled to the negative DC bus through the second switch Q2 and the fourth switch Q4. At this time, if the DC bus is in an unbalanced state, that is, the voltage of the positive bus capacitor Cp or the negative bus capacitor Cn is not equal to 1 / 2Udc, the conduction of the fourth switch Q4 and the first power device Q5 will cause the flying capacitor C to... fly A current loop is formed between the capacitor and the negative bus capacitor Cn, thereby utilizing the flying capacitor C flyThe voltage can be basically stabilized at 1 / 2Udc, and the flying capacitor C fly By charging and discharging the negative bus capacitor Cn, the difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc is reduced, and the potential at the midpoint O of the split capacitor tends to be balanced.

[0089] Specifically, when the voltage across the negative bus capacitor Cn is greater than that across the flying capacitor C fly When the voltage is applied, the negative bus capacitor Cn flows towards the flying capacitor C. fly Charging occurs at the fourth switch Q4, the first power device Q5, and the flying capacitor C. fly In the circuit formed by the negative bus capacitor Cn and the filter inductor L, the current flows from the midpoint O of the split capacitor to the connection point of the first switch Q1 and the second switch Q2. That is, the current flows out of the midpoint O of the split capacitor, which reduces the voltage of the negative bus capacitor Cn, reduces the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, and the potential of the midpoint O of the split capacitor tends to be balanced.

[0090] Similarly, when the voltage across the negative bus capacitor Cn is less than that across the flying capacitor C fly When the voltage is applied, the flying capacitor C fly Charging the negative bus capacitor Cn, at the fourth switch Q4, the first power device Q5, and the flying capacitor C fly In the circuit formed by the negative bus capacitor Cn and the filter inductor L, the current flows from the connection point of the first switch Q1 and the second switch Q2 to the midpoint O of the split capacitor. That is, the current flows into the midpoint O of the split capacitor, which increases the voltage of the negative bus capacitor Cn, reduces the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, and the potential of the midpoint O of the split capacitor tends to be balanced.

[0091] As described above, when both the first power device Q5 and the second power device Q6 in the balancing circuit 12 are fully controllable devices, the balancing circuit 12 can dynamically adjust the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn in real time according to the states of the first switch Q1 and the fourth switch Q4. The balancing circuit 12 has a high control capability and a good ability to adjust the potential of the midpoint O of the split capacitor. In addition, because the balancing circuit 12 has a high control capability, the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn is related to the voltage of the flying capacitor C. fly The voltage difference is small. The voltage across the positive bus capacitor Cp or the voltage across the negative bus capacitor Cn is related to the voltage across the flying capacitor C. fly The voltage difference is the voltage across the filter inductor L. According to the formula for the voltage across the inductor: U = L * di / dt, it can be seen that when the voltage U of the filter inductor L is small and the current conversion rate of the filter inductor L is constant, the value of the filter inductor L can also be small, thus greatly reducing the hardware cost of the balancing circuit 12.

[0092] The following explanation will illustrate the operating principle of the balancing circuit 12 when the DC source is in discharge mode and one of the first and second power devices is a fully controlled device, while the other is a diode. (See also...) Figure 12 , Figure 12 for Figure 6 The topology diagram of the energy storage converter 10 corresponding to (b) is shown below. The topology has been modified for easier understanding, but the overall structure remains unchanged. In the balancing circuit 12, the cathode of the first power device D5 is connected to the flying capacitor C. fly The positive terminal of the first power device D5 is connected to the positive terminal of the second power device Q6, and the anode of the first power device D5 is connected to one end of the second power device Q6.

[0093] See Figure 13 , Figure 13 In Figure (a), when the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5, the waveforms representing the on or off states of the four switches and the two power devices in the balancing circuit of the DC / DC converter circuit 11 are shown. Figure 13 (b) is Figure 12 The diagram shows the topology of the DC / DC converter circuit 11 and the balancing circuit 12 during the T3-T4 period, corresponding to their switching states. Specifically, during the T3-T4 period, the second switch Q2, the fourth switch Q4, and the first power device D5 (diode) are turned on, and the DC power supplied by the DC source is coupled to the negative DC bus through the second switch Q2 and the fourth switch Q4. At this time, if the DC bus is in an unbalanced state, i.e., the voltage of the negative bus capacitor Cn is higher than 1 / 2Udc, the turning on of the fourth switch Q4 and the first power device D5 will cause the flying capacitor C to... fly A current loop is formed between the capacitor and the negative bus capacitor Cn, thereby utilizing the flying capacitor C fly The voltage can be basically stabilized at 1 / 2Udc, and the negative bus capacitor Cn is related to the flying capacitor C. fly Charging reduces the difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc, causing the potential at the midpoint O of the split capacitor to tend to balance.

[0094] Specifically, when the voltage of the negative bus capacitor Cn is higher than that of the flying capacitor C fly When the voltage is applied, the flying capacitor C fly In the circuit consisting of the negative bus capacitor Cn, filter inductor L, first power device D5, and fourth switch Q4, current flows from the midpoint O of the split capacitor to the connection point of the third switch Q3 and the fourth switch Q4, i.e., current flows out of the midpoint O of the split capacitor. This causes the voltage of the negative bus capacitor Cn to decrease, reducing the difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc, and the potential at the midpoint O of the split capacitor tends to balance. However, it is worth noting that because diodes have single-phase conductivity, when the voltage of the negative bus capacitor Cn is lower than that of the flying capacitor C... flyWhen the voltage is low, the first power device D5 is cut off, and the flying capacitor C... fly Since the negative bus capacitor Cn cannot be charged, the balancing circuit 12 cannot regulate (increase) the voltage of the negative bus capacitor Cn.

[0095] It is worth noting that if the cathode and anode of the first power device D5 are swapped (and the switching direction of the second power device Q6 is also swapped) and the second switch Q2 and the fourth switch Q4 are also turned on, then only when the flying capacitor C... fly When the voltage is greater than the voltage of the negative bus capacitor Cn, the flying capacitor C fly A current loop can only be formed between the negative bus capacitor Cn, the filter inductor L, the first power device D5, and the fourth switch Q4, and the flying capacitor C fly Charging the negative bus capacitor Cn increases its voltage, reducing the difference between the voltage of Cn and 1 / 2Udc, causing the potential at the midpoint O of the split capacitor to tend towards equilibrium. However, when the flying capacitor C... fly When the voltage is less than the voltage of the negative bus capacitor Cn, the first power device D5 is cut off, and the balancing circuit 12 cannot play the role of regulating (reducing) the voltage of the negative bus capacitor Cn.

[0096] See Figure 14 , Figure 14 In Figure (a), when the duty cycle D of the DC / DC converter circuit 11 is less than 0.5, the waveforms representing the on or off states of the four switches and the two power devices in the balancing circuit of the DC / DC converter circuit 11 are shown. Figure 14 (b) is Figure 12 The topology diagram shows the corresponding switching states of the DC / DC converter circuit 11 and the balancing circuit 12 during the T0-T1 and T2-T3 periods. Specifically, during the T0-T1 and T2-T3 periods, the third switch Q3, the fourth switch Q4, and the first power device D5 (diode) can be turned on, while the first switch Q1, the second switch Q2, and the second power device Q6 are turned off. The DC power supplied by the DC source is coupled to the negative DC bus through the third switch Q3 and the fourth switch Q4. At this time, if the DC bus is in an unbalanced state, that is, when the voltage of the negative bus capacitor Cn is higher than 1 / 2Udc, the conduction of the fourth switch Q4 and the first power device D5 will cause the flying capacitor C to... fly A current loop is formed between the capacitor and the negative bus capacitor Cn, thereby utilizing the flying capacitor C fly The voltage can be basically stabilized at 1 / 2Udc, and the negative bus capacitor Cn is related to the flying capacitor C. fly Charging reduces the voltage difference between the negative bus capacitor Cn and 1 / 2Udc, causing the potential at the midpoint O of the split capacitor to tend to balance.

[0097] Specifically, when the voltage of the negative bus capacitor Cn is higher than that of the flying capacitor C flyWhen the voltage is applied, the flying capacitor C fly In the circuit consisting of the negative bus capacitor Cn, filter inductor L, first power device D5, and fourth switch Q4, current flows from the midpoint O of the split capacitor to the connection point of the third switch Q3 and the fourth switch Q4, i.e., current flows out of the midpoint O of the split capacitor. This causes the voltage of the negative bus capacitor Cn to decrease, reducing the difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc, and the potential at the midpoint O of the split capacitor tends to balance. However, it is worth noting that because diodes have single-phase conductivity, when the voltage of the negative bus capacitor Cn is lower than that of the flying capacitor C... fly When the voltage is applied, the flying capacitor C fly Since the negative bus capacitor Cn cannot be charged, the balancing circuit 12 cannot regulate (increase) the voltage of the negative bus capacitor Cn.

[0098] It is worth noting that if the cathode and anode of the first power device D5 are swapped (and the switching direction of the second power device Q6 is also swapped) and the third switch Q3 and the fourth switch Q4 are also turned on, then only when the flying capacitor C... fly When the voltage is greater than the voltage of the negative bus capacitor Cn, the flying capacitor C fly A current loop can only be formed between the negative bus capacitor Cn, the filter inductor L, the first power device D5, and the fourth switch Q4, and the flying capacitor C fly Charging the negative bus capacitor Cn increases its voltage, reducing the difference between the voltage of Cn and 1 / 2Udc, causing the potential at the midpoint O of the split capacitor to tend towards equilibrium. However, when the flying capacitor C... fly When the voltage is less than the voltage of the negative bus capacitor Cn, the first power device D5 is cut off, and the balancing circuit 12 cannot play the role of regulating (reducing) the voltage of the negative bus capacitor Cn.

[0099] When the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5, and it is in the time periods T0-T1 and T2-T3, the first switch Q1, the second switch Q2, and the second power device Q6 in the balancing circuit 12 are simultaneously turned on. The DC power supplied by the DC source is coupled to the positive DC bus through the first switch Q1 and the second switch Q2. The working principle of the balancing power in this case is similar to... Figure 8 The operating principle of the balancing circuit 12 shown is the same, and will not be repeated here. When the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5 and is in the T1-T2 time period, the first switch Q1, the third switch Q3, and the second power device Q6 in the balancing circuit 12 are simultaneously turned on. The DC power supplied by the DC source is coupled to the positive DC bus through the third switch Q3 and the first switch Q1. In this case, the operating principle of the balancing circuit 12 is the same as... Figure 9 The working principle of the balancing circuit 12 shown is the same, and will not be described in detail here.

[0100] In addition, when the first power device Q5 in the balancing circuit 12 is a fully controllable device and the second power device D6 is a diode, the working principle of the balancing circuit 12 is similar to that of the balancing circuit 12 when the first power device D5 is a diode and the second power device D6 is a fully controllable device, and will not be elaborated here.

[0101] As described above, when one of the first power device and the second power device is a fully controllable device and the other is a diode, the balancing circuit 12 can only flexibly adjust the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn (either increasing or decreasing the voltage) according to the state of the first switch Q1 or the fourth switch Q4 when the power device corresponding to the fully controllable device is turned on. For the other power device, which is a diode, it can only unidirectionally adjust the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn (either increasing or decreasing only). Whether the voltage of the positive bus capacitor Cp or the negative bus capacitor Cn is increased or decreased depends mainly on the connection state of the cathode and anode of the power device (diode). Therefore, when one of the first power device Q5 and the second power device is a fully controllable device and the other is a diode, the balancing circuit 12 has better control capability and reduces the number of fully controllable devices used, thus lowering costs. In this case, the voltage across the positive bus capacitor Cp and the voltage across the negative bus capacitor Cn are related to the voltage across the flying capacitor C. fly The voltage difference is also smaller, and the value of the filter inductor L can also be smaller, thus greatly reducing the hardware cost of the balancing circuit 12.

[0102] The following explanation will illustrate the operating principle of the balancing circuit 12 when the energy storage battery is in a discharging state and both the first and second power devices are diodes. For easier understanding, please refer to [link to relevant documentation]. Figure 15 , Figure 15 for Figure 6 The diagram shows the topology of the energy storage converter 10 corresponding to (d). The topology has been modified for easier understanding, but the overall structure remains unchanged. In the balancing circuit 12, the first power device D5 and the second power device D6 are connected in reverse series. Specifically, the cathode of the first power device D5 is connected to the flying capacitor C... fly The positive terminal of the first power device is connected to the positive terminal, and the anode of the second power device D6 is connected to the flying capacitor C. fly The negative terminal of the first power device D5 is connected to the negative terminal of the second power device D6, and the anode of the first power device D5 is connected to the cathode of the second power device D6.

[0103] See Figure 16 , Figure 16In Figure (a), when the duty cycle D of the DC / DC converter circuit 11 is less than 0.5, the waveforms representing the on or off states of the four switches and the two power devices in the balancing circuit of the DC / DC converter circuit 11 are shown. Figure 16 Figure (b) shows the topology of the DC / DC converter circuit 11 and the balancing circuit 12 during the T1-T2 period, with corresponding switching states. Specifically, during the T1-T2 period, the first switch Q1, the third switch Q3, and the second power device D6 can be turned on simultaneously. The DC power supplied by the DC source is coupled to the positive DC bus through the first switch Q1 and the third switch Q3. At this time, if the DC bus is in an unbalanced state, that is, when the voltage of the positive bus capacitor Cp is higher than 1 / 2Udc, the turning on of the first switch Q1 and the second power device D6 will cause the flying capacitor C to... fly A current loop is formed between the capacitor and the positive bus capacitor Cp, thereby utilizing the flying capacitor C fly The voltage can be basically stabilized at 1 / 2Udc, and the positive bus capacitor Cp is related to the flying capacitor C. fly Charging reduces the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, causing the potential at the midpoint O of the split capacitor to tend to balance.

[0104] Specifically, when the voltage of the positive bus capacitor Cp is higher than that of the flying capacitor C fly When the voltage is applied, the flying capacitor C fly In the circuit consisting of the positive bus capacitor Cp, filter inductor L, second power device D6, and first switch Q1, current flows from the connection point of third switch Q3 and fourth switch Q4 to the midpoint O of the split capacitor. This current inflow into the midpoint O of the split capacitor lowers the voltage across the positive bus capacitor Cp, reducing the difference between the voltage across Cp and 1 / 2Udc, and causing the potential at the midpoint O of the split capacitor to tend towards equilibrium. However, it is worth noting that because diodes have single-phase conductivity, when the voltage across the positive bus capacitor Cp is lower than that of the flying capacitor C... fly When the voltage is low, the second power device D6 is cut off, and the flying capacitor C... fly Since the positive bus capacitor Cp cannot be charged, the balancing circuit 12 cannot regulate (increase) the voltage of the positive bus capacitor Cp.

[0105] It is worth noting that if the cathode and anode of the second power device D6 are swapped (and the switching direction of the first power device D5 is also swapped) and the first switch Q1 and the third switch Q3 are also turned on, then only when the flying capacitor C... fly When the voltage is greater than the voltage of the negative bus capacitor Cn, the flying capacitor C fly A current loop can only be formed between the negative bus capacitor Cn, the filter inductor L, the second power device D6, and the first switch Q1, and the flying capacitor C... flyCharging the negative bus capacitor Cn increases the voltage of the positive bus capacitor Cp, reducing the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, causing the potential at the midpoint O of the split capacitor to tend towards equilibrium. However, when the flying capacitor C... fly When the voltage is less than the voltage of the negative bus capacitor Cn, the second power device D6 is cut off, and the balancing circuit 12 cannot play the role of regulating (reducing) the voltage of the positive bus capacitor Cp.

[0106] See Figure 17 , Figure 17 In Figure (a), when the duty cycle D of the DC / DC converter circuit 11 is less than 0.5, the waveforms representing the on or off states of the four switches and the two power devices in the balancing circuit of the DC / DC converter circuit 11 are shown. Figure 17 Figure (b) shows the topology of the DC / DC converter circuit 11 and the balancing circuit 12 during the time periods T0-T1 and T2-T3, with corresponding switching states. Specifically, during the time periods T0-T1 and T2-T3, the first switch Q1, the second switch Q2, and the second power device D6 can be turned on, and the DC power supplied by the DC source is coupled to the positive DC bus through the first switch Q1 and the second switch Q2. At this time, if the DC bus is in an unbalanced state, that is, the voltage of the positive bus capacitor Cp on the balancing bridge arm is higher than 1 / 2Udc, the turning on of the first switch Q1 and the second power device D6 will cause the flying capacitor C to... fly A current loop is formed between the capacitor and the positive bus capacitor Cp, thereby utilizing the flying capacitor C fly The voltage can be basically stabilized at 1 / 2Udc, and the positive bus capacitor Cp is related to the flying capacitor C. fly Charging reduces the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, causing the potential at the midpoint O of the split capacitor to tend to balance.

[0107] Specifically, when the voltage of the positive bus capacitor Cp is higher than that of the flying capacitor C fly When the voltage is applied, the flying capacitor C fly In the circuit consisting of the positive bus capacitor Cp, filter inductor L, second power device D6, and first switch Q1, current flows from the connection point of third switch Q3 and fourth switch Q4 to the midpoint O of the split capacitor. This current flows into the midpoint O of the split capacitor, causing the voltage across the positive bus capacitor Cp to decrease. The difference between the positive bus capacitor Cp and 1 / 2Udc decreases, and the potential at the midpoint O of the split capacitor tends to balance. However, it is worth noting that because diodes have single-phase conductivity, when the voltage across the positive bus capacitor Cp is lower than that of the flying capacitor C... fly When the voltage is low, the second power device D6 is cut off, and the flying capacitor C... fly Since the positive bus capacitor Cp cannot be charged, the balancing circuit 12 cannot regulate (increase) the voltage of the positive bus capacitor Cp.

[0108] It is worth noting that if the cathode and anode of the second power device D6 are swapped (and the switching direction of the first power device D5 is also swapped) and the first switch Q1 and the third switch Q3 are also turned on, then only when the flying capacitor C... fly When the voltage is greater than the voltage of the negative bus capacitor Cn, the flying capacitor C fly A current loop can only be formed between the negative bus capacitor Cn, the filter inductor L, the second power device D6, and the first switch Q1, and the flying capacitor C... fly Charging the negative bus capacitor Cn increases the voltage of the positive bus capacitor Cp, reducing the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, causing the potential at the midpoint O of the split capacitor to tend towards equilibrium. However, when the flying capacitor C... fly When the voltage is less than the voltage of the negative bus capacitor Cn, the second power device D6 is cut off, and the balancing circuit 12 cannot play the role of regulating (reducing) the voltage of the positive bus capacitor Cp.

[0109] When the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5 and it is in the T3-T4 time period, the second switch Q2, the fourth switch Q4, and the first power device D5 are turned on. The DC power supplied by the DC source is coupled to the negative DC bus through the second switch Q2 and the fourth switch Q4. The principle of the balancing power supply in this case is the same as... Figure 13 The operating principle of the balancing circuit 12 shown is the same, and will not be repeated here. When the duty cycle D of the DC / DC converter circuit 11 is less than 0.5, and it is in the T0-T1 and T2-T3 time periods, the third switch Q3, the fourth switch Q4, and the first power device D5 are turned on, and the DC power supplied by the DC source is coupled to the negative DC bus through the third switch Q3 and the fourth switch Q4. In this case, the operating principle of the balancing circuit 12 is the same as... Figure 14 The working principle of the balancing circuit 12 shown is the same, and will not be described in detail here.

[0110] As described above, when both the first power device D5 and the second power device D6 in the balancing circuit 12 are diodes, under different switching states of the DC / DC converter circuit 11, the balancing circuit 12 can only operate when the voltage of the positive bus capacitor Cp and the voltage of the negative bus capacitor Cn are greater than or less than the voltage of the flying capacitor C. fly The voltage is adjusted unidirectionally between the positive bus capacitor Cp and the negative bus capacitor Cn to decrease or increase either the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn. Specifically, the connection method of the cathode and anode of the first power device D5 and the second power device D6 in the balancing circuit 12 affects the relationship between the positive bus capacitor Cp and the flying capacitor Cn. fly The main reason for whether a current loop can be formed between them is that when both the first power device D5 and the second power device D6 in the balancing circuit 12 are diodes, the control capability of the balancing circuit 12 is generally average, but its economy is better.

[0111] See Figure 18 , Figure 18 yes Figure 4 The diagrams in (b) and (c) show the topology of the energy storage converter 10. The balancing circuit 12 includes a first power device, a second power device, and a filter inductor L. One of the first and second power devices is a fully controlled device, and the other is a diode. Specifically, one end of the first power device, one end of the second power device, and one end of the filter inductor L are connected to a single point. The other end of the diode power device is... Figure 4 The third terminal of (b) and (c) is connected to either the positive DC bus or the negative DC bus. The other end of the power device, which is a fully controllable device, is... Figure 4 The first or second terminal of (b) and (c) is connected to the midpoint O of the split capacitor or the DC / DC converter circuit 11 (flying capacitor C). fly (The positive or negative terminal) is connected.

[0112] When the energy storage battery is in discharge mode, the first power device D5 in the balancing circuit 12 is a diode, the second power device Q6 is a fully controlled device, and the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5. During the T0-T1 and T2-T3 time periods, if... Figure 19 As shown in (a) or (c), the first switch Q1, the second switch Q2, and the second power device Q6 are turned on, and the DC power supplied by the DC source is coupled to the positive DC bus through the first switch Q1 and the second switch Q2. Since the second power device Q6 is a fully controllable device, the first switch Q1, the positive bus capacitor Cp, the second power device Q6, the filter inductor L, and the flying capacitor C are all connected. fly In the formed current loop, the direction of current flow is unrestricted. For example, when the voltage across the positive bus capacitor Cp is higher than 1 / 2Udc, the current flows through the flying capacitor C... fly In the circuit consisting of the positive bus capacitor Cp, the filter inductor L, the second power device Q6, and the first switch Q1, current flows from the midpoint O of the split capacitor to the connection point of the first switch Q1 and the second switch Q2. That is, current flows into the midpoint O of the split capacitor, causing the voltage of the positive bus capacitor Cp to decrease. The difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc decreases, and the potential at the midpoint O of the split capacitor tends to balance. Similarly, when the voltage of the positive bus capacitor Cp is lower than that of the flying capacitor C... fly When the voltage is applied, the flying capacitor C fly In the circuit consisting of the positive bus capacitor Cp, the filter inductor L, the second power device Q6, and the first switch Q1, the current flows from the connection point of the first switch Q1 and the second switch Q2 to the midpoint O of the split capacitor, that is, the current flows out of the midpoint O of the split capacitor, which increases the voltage of the positive bus capacitor Cp, reduces the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc, and the potential of the midpoint O of the split capacitor tends to be balanced.

[0113] like Figure 20 As shown in (a) or (c), when the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5 and is in the T1-T2 time period, the first switch Q1, the third switch Q3, and the second power device Q6 are turned on. The DC power supplied by the DC source is coupled to the positive DC bus through the first switch Q1 and the third switch Q3. The first switch Q1, the positive bus capacitor Cp, the second power device Q6, the filter inductor L, and the flying capacitor C are all connected. fly This forms a current loop. When the voltage across the positive bus capacitor Cp is higher than that across the flying capacitor C... fly When the voltage is applied, the positive bus capacitance Cp flows towards the flying capacitor C. fly During charging, current flows into the midpoint O of the split capacitor, causing the voltage across the positive bus capacitor Cp to drop. The DC bus voltage tends to balance. When the voltage across the positive bus capacitor Cp is lower than that of the flying capacitor C... fly When the voltage is applied, the flying capacitor C fly When the positive bus capacitor Cp is charged, current flows out of the midpoint O of the split capacitor, the voltage of the positive bus capacitor Cp rises, and the DC side bus voltage tends to balance.

[0114] When the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5 and it is in the T3-T4 time period, the second power device Q6 is not conducting, while the second switch Q2 and the fourth switch Q4 are conducting. Due to the presence of the filter inductor L, the current in the balancing circuit 12 cannot change abruptly, and the first power device D5 acts as a freewheeling current. Similarly, when the duty cycle D of the DC / DC converter circuit 11 is less than 0.5 and it is in the T0-T1 and T2-T3 time periods, the second power device Q6 is not conducting, while the third switch Q3 and the fourth switch Q4 are conducting, and the first power device D5 also acts as a freewheeling current.

[0115] When the energy storage battery is in discharge mode, the first power device Q5 in the balancing circuit 12 is a fully controlled device, the second power device D6 is a diode, and the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5. During the T3-T4 time period, if... Figure 19 As shown in (b) and (d), the second switch Q2, the fourth switch Q4, and the first power device Q5 are simultaneously turned on. The DC power supplied by the DC source is coupled to the negative DC bus through the second switch Q2 and the fourth switch Q4. Since the first power device Q5 is a fully controlled device, the fourth switch Q4, the negative bus capacitor Cn, the first power device Q5, the filter inductor L, and the flying capacitor C are all connected. fly In the formed current loop, the direction of current flow is unrestricted. For example, when the voltage across the negative bus capacitor Cn is higher than 1 / 2Udc, and the difference between the voltage across the negative bus capacitor Cn and 1 / 2Udc is greater than a first preset value, the current flows through the flying capacitor C... flyIn the circuit consisting of the negative bus capacitor Cn, the filter inductor L, the first power device Q5, and the fourth switch Q4, the current flows from the midpoint O of the split capacitor to the connection point of the third switch Q3 and the fourth switch Q4 in the DC / DC converter circuit 11. That is, the current flows out of the midpoint O of the split capacitor, causing the voltage of the negative bus capacitor Cn to decrease. The difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc decreases, and the potential at the midpoint O of the split capacitor tends to balance. Similarly, when the voltage of the negative bus capacitor Cn is lower than that of the flying capacitor C... fly When the voltage is applied, the flying capacitor C fly In the circuit consisting of the negative bus capacitor Cn, the filter inductor L, the first power device Q5, and the fourth switch Q4, the current flows from the connection point of the first switch Q1 and the second switch Q2 to the midpoint O of the split capacitor. That is, the current flows into the midpoint O of the split capacitor, which increases the voltage of the negative bus capacitor Cn and reduces the difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc. The potential of the midpoint O of the split capacitor tends to be balanced.

[0116] like Figure 20 As shown in (b) or (d), when the duty cycle D of the DC / DC converter circuit 11 is less than 0.5 and is in the T0-T1 and T2-T3 time periods, the third switch Q3, the fourth switch Q4, and the first power device Q5 are simultaneously turned on. The DC power supplied by the DC source is coupled to the negative DC bus through the third switch Q3 and the fourth switch Q4. The fourth switch Q4, the negative bus capacitor Cn, the first power device Q5, the filter inductor L, and the flying capacitor C fly A current loop is formed when the voltage across the negative bus capacitor Cn is higher than that across the flying capacitor C. fly When the voltage is applied, the negative bus capacitor Cn flows towards the flying capacitor C. fly During charging, current flows out of the midpoint O of the split capacitor, causing the voltage of the negative bus capacitor Cn to drop. The potential at the midpoint O of the split capacitor tends to balance. When the voltage of the negative bus capacitor Cn is lower than that of the flying capacitor C... fly When the voltage is applied, the flying capacitor C fly As the positive bus capacitor Cp is charged, current flows into the midpoint O of the split capacitor, the voltage of the positive bus capacitor Cp rises, and the DC side bus voltage tends to balance.

[0117] When the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5 and is in the time periods T0-T1 and T2-T3, the first power device Q5 is not conducting, while the first switch Q1 and the second switch Q2 are conducting. Due to the presence of the filter inductor L, the current in the balancing circuit 12 cannot change abruptly, and the second power device D6 acts as a freewheeling current. Similarly, when the duty cycle D of the DC / DC converter circuit 11 is greater than 0.5 and is in the time period T1-T2, the first power device Q5 is not conducting, while the first switch Q1 and the third switch Q3 are conducting, and the second power device D6 also acts as a freewheeling current.

[0118] As described above, for example... Figure 18 In the energy storage converter 10 shown, the power devices corresponding to the diodes in the balancing circuit 12 act as freewheeling current. The power devices corresponding to the fully controlled devices achieve the same on or off state as some switches (first switch Q1 or fourth switch Q4) in the DC / DC converter circuit 11, thus enabling the flying capacitor C. fly The current conducts between the positive bus capacitor Cp or the negative bus capacitor Cn, and can then flow through the flying capacitor C. fly The voltage of the positive bus capacitor Cp or the negative bus capacitor Cn is stabilized by charging and discharging the positive bus capacitor Cp or the negative bus capacitor Cn. In summary, this balancing circuit 12 has good control capability and good economy.

[0119] Furthermore, to reduce the losses in the balancing circuit 12, a selector switch (not shown in the figure) can be provided between the balancing circuit 12 and the midpoint O of the split capacitor. The selector switch includes, for example, Figure 21 The diagram illustrates mechanical switches, active semiconductor devices, passive semiconductor devices, and combinations thereof. Specifically, when the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn differs from 1 / 2Udc, the selector switch closes, and the balancing circuit 12 cooperates with the DC / DC converter circuit 11 to stabilize the voltage of the positive bus capacitor Cp and / or the voltage of the negative bus capacitor Cn. When the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn is the same as 1 / 2Udc, the selector switch opens, the balancing circuit 12 does not operate, the losses of the balancing circuit 12 are reduced, and its service life is extended.

[0120] It should be noted that the DC / AC conversion circuit topology provided in this application includes, for example: Figure 22 The type I three-level topology shown in (a) is as follows: Figure 22 The active NPC three-level topology (ANPC) shown in (b) and as shown in [other diagrams] Figure 22 The T-type three-level topology shown in (c) is not limited in this application. Furthermore, as mentioned above, the three-level DC / AC converter circuit topology provided in this application is for descriptive convenience only. In practical applications, the three-level DC / AC converter circuit topology can be expanded to other multi-level DC / AC converter circuit topologies. No specific limitations are made here; selection can be made according to specific circumstances, and all are within the protection scope of this application.

[0121] In some possible implementations, such as Figure 23As shown, the two-stage energy storage converter 10 includes N DC / DC converter circuits and M DC / AC converter circuits, where N and M are both greater than 1. When the DC source is in discharge mode, the DC input side of each DC / DC converter circuit is connected to the DC source, the DC output side of each DC / DC converter circuit is connected to the DC bus, the DC input side of each DC / AC converter circuit is connected to the DC bus, and the AC output side of each DC / AC converter circuit is connected to the AC bus. The topology of the DC / DC converter circuit 11 is as follows: Figure 5 As shown, the topology of DC / AC converter circuit 13 is as follows: Figure 22 As shown in any one of the embodiments. That is to say, the topology of the power conversion circuit in this type of energy storage converter 10 is the same as that in the aforementioned embodiments of this application, the only difference being that there are more DC / DC conversion circuits and DC / AC conversion circuits. Therefore, it also faces the problem of potential fluctuation at the midpoint O of the split capacitor.

[0122] To address this problem, X circuits provided in this application can be set between N DC / DC conversion circuits and M DC / AC conversion circuits. Figure 6 and / or as Figure 18 The balanced circuit 12 is shown, where 1 ≤ X ≤ M. For example, as shown... Figure 24 As shown, any one of the following can be set between DC / DC converter circuit #1 and DC / AC converter circuit #1: Figure 6 The balancing circuit 12#1 shown includes three terminals, two of which are connected to the DC / DC converter circuit #1, and one terminal is connected to the midpoint O of the split capacitor on the DC side of the DC / AC converter circuit #1. When the absolute value of the difference between the voltage of the positive bus capacitor Cp1 or the voltage of the negative bus capacitor Cn1 and 1 / 2Udc is greater than a first preset value, the power devices in the balancing circuit 12#1 cooperate with the switches in the DC / DC converter circuit #1 to cause the flying capacitor C of the DC / DC converter circuit #1 to... fly A current loop is formed with the positive bus capacitor Cp1 or the negative bus capacitor Cn1 of the split capacitor to balance the potential at the midpoint O1 of the split capacitor. To reduce the number of balancing circuits 12 used and decrease hardware costs, the midpoint O of the split capacitor in DC / AC converter circuit #1 can be connected to the midpoint O of the other M-1 split capacitors via wires to balance the potential at the midpoint O of the other M-1 split capacitors. Similarly, any one of the following can be set between DC / DC converter circuit #1 and DC / AC converter circuit #2: Figure 18The balancing circuit 12#1 shown has three terminals. One terminal is connected to the DC / DC converter circuit #1, one terminal is connected to the midpoint O of the split capacitor, and the other terminal is connected to either the positive or negative DC bus. The operating principle of this balancing circuit 12 is not detailed here. To better balance the potential of the midpoint O of the split capacitors on the DC side of each DC / AC converter circuit in the energy storage converter 10, more balancing circuits 12 can be provided. This application does not limit the number of balancing circuits 12 used. One balancing circuit 12 corresponds to one DC / DC converter circuit and one DC / AC converter circuit, and the midpoint O of each split capacitor in the system are interconnected.

[0123] Additionally, it should be noted that in all the above embodiments, if the first power device and the second power device in the balancing circuit 12 are not both diodes, the energy storage converter 10 also includes a controller 101. For example... Figure 25 As shown, the controller 101 is electrically connected to the DC / DC converter circuit 11. Optionally, the controller 101 can also be wirelessly connected to the DC / DC converter circuit 11. The specific connection can be determined according to the actual application scenario, and this application does not impose any restrictions on this.

[0124] For example, when both the first power device Q5 and the second power device Q6 are fully controllable devices, the controller 101 controls the first power device Q5 to have the same on and off states as the fourth switch Q4, and the second power device Q6 to have the same on and off states as the first switch Q1, so that the fourth switch Q4, the first power device Q5, and the flying capacitor C... fly The negative bus capacitor Cn forms a current loop, thereby reducing the difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc, or, to make the first switch Q1, the second power device Q6, and the flying capacitor C... fly The current loop is formed between the positive bus capacitor Cp and the positive bus capacitor Cp, thereby reducing the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc.

[0125] For example, when the first power device Q5 is a fully controllable device and the second power device D6 is a diode, the controller 101 controls the first power device Q5 and the fourth switch Q4 to have the same on and off states, so that the fourth switch Q4, the first power device Q5, and the flying capacitor C... fly The negative bus capacitor Cn forms a current loop, thereby reducing the difference between the voltage of the negative bus capacitor Cn and 1 / 2Udc.

[0126] For example, when the first power device D5 is a diode and the second power device Q6 is a fully controllable device, the controller 101 is used to control the second power device Q6 to have the same on and off states as the first switch Q1, so that the first switch Q1, the second power device Q6, and the flying capacitor C... flyThe current loop is formed between the positive bus capacitor Cp and the positive bus capacitor Cp, thereby reducing the difference between the voltage of the positive bus capacitor Cp and 1 / 2Udc.

[0127] It should also be noted that in all the above embodiments, if there is a switch between the balancing circuit 12 and the midpoint O of the split capacitor, the energy storage converter 10 further includes a controller 101. When the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn is the same as 1 / 2Udc, the controller 101 controls the switch to open to reduce the loss of the balancing circuit 12. When the voltage of the positive bus capacitor Cp or the voltage of the negative bus capacitor Cn is different from 1 / 2Udc, the controller 101 controls the switch to close to balance the potential of the midpoint O of the split capacitor.

[0128] In summary, the embodiments proposed in this application can maintain the power devices in the balancing circuit 12 and some switches in the DC / DC converter circuit 11 in the same on or off state under different switching states of the DC / DC converter circuit 11, so that the flying capacitor C in the DC / DC converter circuit 11 can be kept in the same on or off state. fly A current loop is formed between the positive bus capacitor Cp or the negative bus capacitor Cn, and the flying capacitor C is utilized. fly The voltage can be basically stabilized at 1 / 2Udc, and the voltage of the positive bus capacitor Cp or the negative bus capacitor Cn can be dynamically adjusted to achieve the balance of the potential at the midpoint O of the split capacitor.

[0129] This application embodiment also provides a control method for a balancing circuit. The method includes: controlling the first power device and the second power device in the balancing circuit to have the same on and off states as the first switch, the second switch, the third switch, and the fourth switch in the DC / DC converter circuit, so that a current loop is formed between the flying capacitor and the positive bus capacitor or the negative bus capacitor in the DC / DC converter circuit, and the difference between the positive bus capacitor voltage or the negative bus capacitor voltage and 1 / 2Udc is reduced.

[0130] See Figure 26 , Figure 26 The diagram shown illustrates a control method for a balanced circuit, which includes:

[0131] S201: Detect the status of the first switch and the fourth switch;

[0132] S202: Control the second power device to be in the same on or off state as the first switch;

[0133] S203: Control the second power device to be in the same on or off state as the first switch.

[0134] When a switch is installed between the balancing circuit and the connection points of the positive and negative bus capacitors, see [reference needed]. Figure 27 , Figure 27The diagram shown is a schematic of a control method for a balanced circuit. This control method also includes:

[0135] S301: Determine whether the positive bus capacitor voltage or the negative bus capacitor voltage is equal to 1 / 2Udc;

[0136] S302: If the voltage of the positive bus capacitor or the voltage of the negative bus capacitor is equal to 1 / 2Udc, control the above switch to open in order to reduce the loss of the balancing circuit.

[0137] S303: If the positive bus capacitor voltage or the negative bus capacitor voltage is equal to 1 / 2Udc, control the above switch to close, so as to reduce the difference between the bus capacitor voltage or the negative bus capacitor voltage and 1 / 2Udc.

[0138] This application achieves the ability of the energy storage converter 10 to handle harmonic loads, unbalanced loads, and half-wave rectified loads under both grid-connected and off-grid conditions through topology optimization, thus expanding its application scenarios. Moreover, compared to... Figure 3 The balancing circuit shown in (b) has a simple structure, requires fewer components, and the power devices are subjected to less voltage stress, resulting in higher reliability. At the same time, the filter inductor in the balancing circuit 12 is also smaller, which greatly reduces material costs and improves economic efficiency.

[0139] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solution of the present invention should be included within the scope of protection of the present invention.

Claims

1. An energy storage converter, characterized by, The energy storage converter includes: a DC / DC converter circuit, a balancing circuit, a split capacitor, and a DC / AC converter circuit. The DC / DC conversion circuit includes a flying capacitor and a first switch, a second switch, a third switch, and a fourth switch connected in series. The first switch is connected to the positive DC bus, and the fourth switch is connected to the negative DC bus. The series connection point of the first switch and the second switch is connected to the series connection point of the third switch and the fourth switch through the flying capacitor. The split capacitor includes a positive bus capacitor and a negative bus capacitor connected in series. The positive bus capacitor is connected to the midpoint of the split capacitor and the positive DC bus, and the negative bus capacitor is connected to the midpoint of the split capacitor and the negative DC bus. The positive DC bus, the negative DC bus, and the midpoint of the split capacitor are connected to the DC / AC conversion circuit. The balancing circuit includes a first power device, a second power device, and a filter inductor. The balancing circuit is connected to the midpoint of the DC / DC converter circuit and the split capacitor. The balancing circuit is used to form a current loop between the flying capacitor and the positive bus capacitor, or between the flying capacitor and the negative bus capacitor, so as to reduce the difference between the voltage of the positive bus capacitor or the voltage of the negative bus capacitor and half of the DC bus voltage.

2. The energy storage converter as described in claim 1, characterized in that, The balancing circuit includes three terminals: the first terminal is connected to the midpoint of the split capacitor, the second terminal is connected to the positive terminal of the flying capacitor, and the third terminal is connected to the negative terminal of the flying capacitor.

3. The energy storage converter as described in claim 2, characterized in that, In the balancing circuit, one end of the first power device and one end of the second power device are connected; the other end of the first power device is the second terminal, which is connected to the positive terminal of the flying capacitor; the other end of the second power device is the third terminal, which is connected to the negative terminal of the flying capacitor; the series connection point of the first power device and the second power device is connected to one end of the filter inductor; the other end of the filter inductor is the first terminal, which is connected to the midpoint of the split capacitor.

4. The energy storage converter as described in claim 1, characterized in that, The balancing circuit includes three terminals: the first terminal is connected to the midpoint of the split capacitor, the second terminal is connected to the positive or negative terminal of the flying capacitor, and the third terminal is connected to the positive or negative DC bus.

5. The energy storage converter as described in claim 4, characterized in that, In the balanced circuit, one end of the first power device, one end of the second power device, and one end of the filter inductor are connected to a single point.

6. The energy storage converter as described in claim 5, characterized in that, The first power device is a fully controllable device, the second power device is a diode, the other end of the first power device is the second terminal, which is connected to the positive terminal of the flying capacitor, and the other end of the second power device is the third terminal, which is connected to the negative DC bus; the other end of the filter inductor is the first terminal, which is connected to the midpoint of the split capacitor, or; The other end of the first power device is the first terminal, which is connected to the midpoint of the split capacitor. The other end of the second power device is the third terminal, which is connected to the positive DC bus. The other end of the filter inductor is the second terminal, which is connected to the positive terminal of the flying capacitor.

7. The energy storage converter as described in claim 5, characterized in that, The first power device is a diode, the second power device is a fully controlled device, the other end of the first power device is the third terminal connected to the negative DC bus, the other end of the second power device is the first terminal connected to the midpoint of the split capacitor; the other end of the filter inductor is the second terminal connected to the negative terminal of the flying capacitor, or; The other end of the first power device is the third terminal, which is connected to the positive DC bus. The other end of the second power device is the second terminal, which is connected to the negative terminal of the flying capacitor. The other end of the filter inductor is the first terminal, which is connected to the midpoint of the split capacitor.

8. The energy storage converter as described in claim 3, characterized in that, Both the first power device and the second power device are diodes. The first power device and the second power device are connected in reverse series to form a current loop between the first switch, the flying capacitor, the second power device, and the positive bus capacitor. The difference between the voltage of the positive bus capacitor and half of the DC bus voltage is reduced, or; This creates a current loop between the fourth switch, the flying capacitor, the first power device, and the negative bus capacitor, reducing the difference between the voltage of the negative bus capacitor and half of the DC bus voltage.

9. The energy storage converter as described in claim 3, characterized in that, Both the first power device and the second power device are fully controllable devices. The energy storage converter also includes a controller. The controller is used to control the first power device and the fourth switch to be turned on, so that a current loop is formed between the fourth switch, the flying capacitor, the first power device, and the negative bus capacitor, and the difference between the voltage of the negative bus capacitor and half of the DC bus voltage is reduced.

10. The energy storage converter as described in claim 3, characterized in that, Both the first power device and the second power device are fully controllable devices. The energy storage converter also includes a controller. The controller is used to control both the second power device and the first switch to be turned on, so that a current loop is formed between the first switch, the flying capacitor, the second power device, and the positive bus capacitor, and the difference between the voltage of the positive bus capacitor and half of the DC bus voltage is reduced.

11. The energy storage converter as described in claim 3 or 6, characterized in that, In the balancing circuit, the first power device is a fully controlled device, the second power device is a diode, and the energy storage converter also includes a controller. The controller is used to control the first power device and the fourth switch to be turned on, so that a current loop is formed between the fourth switch, the flying capacitor, the first power device, and the negative bus capacitor, and the difference between the voltage of the negative bus capacitor and half of the DC bus voltage is reduced.

12. The energy storage converter as described in claim 3 or 7, characterized in that, In the balancing circuit, the first power device is a diode, the second power device is a fully controlled device, and the energy storage converter also includes a controller. The controller is used to control the second power device and the first switch to be turned on, so that a current loop is formed between the first switch, the flying capacitor, the second power device, and the positive bus capacitor, and the difference between the voltage of the positive bus capacitor and half of the DC bus voltage is reduced.

13. The energy storage converter as described in any one of claims 1-10, characterized in that, The energy storage converter also includes a controller and a switch, the switch being disposed between the midpoint of the balancing circuit and the split capacitor; The controller is configured to open the switch in response to the positive bus capacitor voltage or the negative bus capacitor voltage being equal to half the DC bus voltage; or The controller is used to control the switch to close in response to the positive bus capacitor voltage or the negative bus capacitor voltage being unequal to half of the DC bus voltage.

14. An energy storage system, characterized in that, The energy storage system includes the energy storage converter and the energy storage battery as described in any one of claims 1-13; The energy storage battery is connected to the DC / DC conversion circuit in the energy storage converter. The energy storage converter is used to realize bidirectional conversion between AC and DC power, converting DC power from the energy storage battery or photovoltaic module into AC power and transmitting the AC power to the power grid or load, or converting AC power from the power grid into DC power to charge the energy storage battery.

15. A control method for a balanced circuit, characterized in that, It is applied to an energy storage converter, which includes: a DC / DC conversion circuit, a balancing circuit, a split capacitor, and a DC / AC conversion circuit; The DC / DC conversion circuit includes a flying capacitor and a first switch, a second switch, a third switch, and a fourth switch connected in series. The first switch is connected to the positive DC bus, and the fourth switch is connected to the negative DC bus. The series connection point of the first switch and the second switch is connected to the series connection point of the third switch and the fourth switch through the flying capacitor. The split capacitor includes a positive bus capacitor and a negative bus capacitor connected in series. The positive bus capacitor is connected to the midpoint of the split capacitor and the positive DC bus, and the negative bus capacitor is connected to the midpoint of the split capacitor and the negative DC bus. The positive DC bus, the negative DC bus, and the midpoint of the split capacitor are connected to the DC / AC conversion circuit. The method includes: The first and second power devices in the control balance circuit and the first, second, third, and fourth switches in the DC / DC converter circuit are turned on and off, so that a current loop is formed between the flying capacitor and the positive or negative bus capacitor in the DC / DC converter circuit, and the difference between the positive or negative bus capacitor voltage and half of the bus voltage is reduced.

16. The method as described in claim 15, characterized in that, The method includes: The first power device and the fourth switch are both turned on, so that a current loop is formed between the fourth switch, the flying capacitor, the first power device, and the negative bus capacitor, and the difference between the voltage of the negative bus capacitor and half of the DC bus voltage is reduced.

17. The method as described in claim 15, characterized in that, The method includes: The second power device and the first switch are both turned on, so that a current loop is formed between the first switch, the flying capacitor, the second power device, and the positive bus capacitor, and the difference between the positive bus capacitor voltage and half of the DC bus voltage is reduced.

18. The method as described in claim 15, characterized in that, A switch is provided between the balancing circuit and the connection point of the positive bus capacitor and the negative bus capacitor, and the method includes: In response to the positive bus capacitor voltage or negative bus capacitor voltage being unequal to half the DC bus voltage, the switch is controlled to close; or The switch is controlled to open in response to the positive bus capacitor voltage or the negative bus capacitor voltage being equal to half of the DC bus voltage.

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