A DC converter and a control method thereof

Abstract

The present invention discloses a DC converter and a control method thereof, comprising a plurality of capacitor voltage dividers connected in series, a plurality of non-isolated balancing units and one or more power unit submodules. The capacitor voltage divider performs voltage balancing through the non-isolated balancing unit and can be used as an input bus capacitor to provide energy for the power unit submodule. Each balancing unit requires at least two diodes, two switching tubes and one energy storage capacitor, and can be cascaded and expanded. By connecting the output ends of the power unit submodules in series or in parallel to form a single or multiple output ports, the DC converter can achieve high-ratio isolated step-down, input series output series isolated step-up or independent power supply; if the voltage is input to only one capacitor voltage divider, all the bus capacitors in series directly provide output, and non-isolated high-ratio step-up can be achieved. The present invention does not require a high-insulation transformer; regardless of whether the balancing unit is open-loop or closed-loop controlled, it is easy to achieve natural voltage balancing of the capacitor voltage divider.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a direct current converter and a control method thereof. Background Art

[0002] The submarine observation network is a DC distributed power system. Shore-based power supplies convert low-voltage AC power to medium-voltage or high-voltage DC power, which is then transmitted to the submarine power supply via submarine cables. The submarine power supply then converts medium-voltage or high-voltage DC power to low-voltage DC power to power various devices. The commonly used voltage level for submarine cable transmission has risen to 10kVDC, posing a challenge to the design of auxiliary power supplies for the submarine power supply. Using medium- and high-voltage DC bus voltage as the auxiliary power supply input offers numerous advantages, including simplified wiring, reduced secondary circuit electromagnetic interference, and improved line insulation. Furthermore, applications such as renewable energy generation and solid-state transformers require high-voltage converter inputs or outputs. Applications such as downhole power supplies and microwave power supplies require DC converters with high step-up ratios, necessitating the research of high-DC-to-DC converters and their control methods.

[0003] In medium- and high-voltage applications, three common configurations are power device series, modular input series, and multi-unit cascade converters. Power device series requires consideration of static and dynamic voltage balancing between multiple switches and the supply of initial drive signals, resulting in complex control strategies, high technical requirements, and high costs. Modular input series can withstand high voltages, reduce power device stress, and facilitate heat dissipation design and system expansion. However, these configurations present the following challenges: First, input voltage balancing across modules. When the input bus voltage divider capacitor is loaded with a constant power load, its input impedance exhibits a negative impedance characteristic, causing the input voltage of each module to diverge. Second, control power for the power unit submodules is difficult to obtain. If power is drawn from the input bus voltage divider capacitor as an auxiliary power supply, the auxiliary power supply also acts as a constant power load, causing the input voltage of each module to diverge. Third, when a module fails and bypasses, it can cause significant voltage and current surges to other power units. Fourth, the power unit requires a high-insulation transformer. Compared to conventional transformers, the engineering design and control of its leakage inductance and parasitic parameters are significantly more difficult, significantly increasing the converter design cost. Fifth, closed-loop output voltage control requires sampling the output voltage for cross-high voltage feedback comparison. The multi-unit cascade converter realizes energy exchange between busbar voltage divider capacitors by cascading busbar voltage divider capacitors with balancing units (units that achieve voltage balance between input and output ends), thereby ensuring voltage balance of each busbar voltage divider capacitor while achieving high transformation ratio voltage reduction or boost.

[0004] The invention patent application "A High-Voltage Power Supply Circuit (CN107276393A)" proposes a cascade-structured converter. This uses an isolated DC-DC converter with balanced voltages to automatically balance the voltages of the two voltage-dividing capacitors at the input, thereby expanding the system's input voltage and achieving a high step-down ratio. However, due to the use of an isolated DC-DC converter, the balancing unit between the capacitor voltage dividers adopts an isolated topology, and the design of a high-insulation transformer is also required when inputting high voltage. Furthermore, the busbar voltage-dividing capacitors within the isolated balancing unit need to be sampled for closed-loop control. Furthermore, power can only be output by the subsequent power unit cascaded across one capacitor voltage divider, preventing power expansion and limiting its practical application to higher voltages.

[0005] The invention patent application "Dual-input DC converter using non-isolated pulse voltage source unit" (CN102437741A) belongs to the technical field of dual-input voltage source. There can only be two power sources, independent or combined, and then output power to the load end through a transformer, that is, there can only be two bus voltage-dividing capacitors or power sources and one output port. The voltage of the two voltage sources is limited by the voltage stress of the switching tube inside the construction unit and the voltage source, and the output voltage of the voltage source. At the same time, although this solution uses a non-isolated balancing unit (non-isolated pulse voltage unit) to construct a DC converter, it requires an inductor to construct a resonant circuit, resulting in a large circuit volume and high cost. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a DC converter and a control method thereof in view of the shortcomings of the existing technology, which can expand the voltage level of the voltage divider capacitor while ensuring low voltage stress of the switch tube in the switch module.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is: a DC converter, comprising:

[0008] Multiple voltage-dividing capacitors connected in series;

[0009] The positive electrode of the i-th voltage-dividing capacitor is connected to the positive input terminal of the i-th balancing unit, and the negative electrode of the i-th voltage-dividing capacitor is connected to the negative input terminal of the i-th balancing unit;

[0010] The positive output terminal of the i-th balancing unit is connected to the positive electrode of the i+1-th voltage-dividing capacitor, and the negative output terminal of the i-th balancing unit is connected to the negative electrode of the i+1-th voltage-dividing capacitor;

[0011] The i-th balancing unit is cascaded with the i+1-th balancing unit;

[0012] The balancing unit includes at least one balancing module; the balancing module includes an energy storage module; the energy storage module is connected in parallel with the input side switch module and the output side switch module;

[0013] Wherein, 1≤i≤n-1, and n is the number of voltage divider capacitors.

[0014] The balancing unit in the present invention has a non-isolated topology structure, does not require a high-insulation transformer, has a simple topology, and can achieve cascade expansion. While ensuring low voltage stress on the switch tube in the switch module, it expands the voltage level of the voltage divider capacitor. At the same time, the balancing unit only requires internal open-loop control, and there is no communication connection between the balancing units. It has high flexibility and can be expanded according to the voltage level of the converter.

[0015] In the present invention, each of the first to n-1th voltage-dividing capacitors is connected to at least one power unit; the output ends of all power units are connected in parallel or in series to form the output end of the DC converter; or the output ends of multiple power units correspond to the multiple output ends of the DC converter. The number of power units is independent of the number of voltage-dividing capacitors and can be expanded according to the power level of the converter; the output ends of all power units are connected in parallel to form the output end of the DC converter, which can achieve high-ratio isolated step-down of the DC converter; the output ends of all power units are connected in series to form the output end of the DC converter, which can achieve input-series-output-series isolated step-up of the DC converter; the output ends of multiple power units correspond to the multiple output ends of the DC converter, which can achieve independent power supply of the multiple output ends of the DC converter.

[0016] The first voltage-dividing capacitor is connected to the two power units to achieve power expansion.

[0017] The power unit is connected to the corresponding voltage-dividing capacitor via a switching switch. By connecting the switching switch in series at the power unit input, the power unit can achieve redundant backup without considering the risk of voltage divergence of the voltage-dividing capacitor. When a power unit fails, it can be directly disconnected from the voltage-dividing capacitor. When the output power level of the DC converter needs to be increased, the power unit can be directly switched on.

[0018] The first voltage divider capacitor is connected to one of the power units through an output-side balancing unit. The two ends of each energy storage capacitor in the output-side balancing unit can serve as the input of the power unit to achieve power expansion.

[0019] The branches formed by the multiple series-connected voltage-dividing capacitors serve as the output terminals of the DC converter. The nth voltage-dividing capacitor is connected to the positive and negative terminals of the power supply, respectively. By applying voltage to only one voltage-dividing capacitor, the branches formed by all the series-connected voltage-dividing capacitors directly provide the output of the DC converter, enabling non-isolated high-ratio voltage boosting.

[0020] The energy storage module is an energy storage capacitor; the input-side switch module includes a first switch tube, the first switch tube is connected in series with a first diode, the first diode is connected in parallel with the energy storage capacitor, and a third diode is connected between the anode of the first diode and the negative electrode of the energy storage capacitor; or the input-side switch module includes a first switch tube, the first switch tube is connected to the positive electrode of the energy storage capacitor, and the negative electrode of the energy storage power supply is connected to the third diode;

[0021] The output side switch module includes a second switch tube, the second switch tube is connected in series with a second diode, the second diode is connected in parallel with the energy storage capacitor, and the anode of the second diode is connected to a fourth diode; or, the output side switch module includes a second switch tube, the positive electrode of the energy storage capacitor is connected to the second switch tube, and the negative electrode of the energy storage capacitor is connected to the fourth diode.

[0022] The balancing unit has a simple structure, low cost, and can be cascaded and expanded. The energy storage module is a single capacitor or multiple capacitors in parallel. The switch module only needs to perform open-loop control to achieve energy transfer and voltage balance at the input and output ends of the balancing unit.

[0023] When the balancing unit includes multiple balancing modules, for two adjacent balancing modules connected in series, the output side switch module of the first balancing module serves as the input side switch module of the second balancing module, which greatly improves the flexibility of cascade expansion.

[0024] When performing isolated high-ratio step-down or isolated boost, the auxiliary power supply for the non-isolated balancing unit is provided by a capacitor voltage divider connected in parallel at its output. When performing non-isolated high-ratio step-up, the auxiliary power supply for the non-isolated balancing unit is provided by a capacitor voltage divider connected in parallel at its input. When the switching transistors in the switching module within the balancing unit are activated, energy is transferred between the voltage divider capacitor and the energy storage capacitor, or between the energy storage capacitors, compensating for the voltage drop caused by the auxiliary power supply circuit drawing energy from the voltage divider capacitor, thereby completing energy transfer and voltage balancing.

[0025] As an inventive concept, the present invention further provides a control method for the above-mentioned DC converter, which includes:

[0026] Each balancing unit is connected to a self-oscillation unit;

[0027] In open-loop mode, the switches in all balancing units operate at a fixed duty cycle and switching frequency. Each switch in a single balancing unit is turned on sequentially, with a dead time between the turn-off time of the previous switch and the turn-on time of the next switch. The switching signal is generated by a self-oscillating unit connected to the balancing unit.

[0028] In the closed-loop mode, the balancing unit first works in the open-loop mode. After the output voltage of each power unit is stable, it supplies power to the main controller. The total output voltage of the DC converter is sampled and conditioned to a sample value V o Sent to the main controller, set the output voltage reference value V ref With V o After the difference is controlled by PI, the control voltage V c , by controlling the voltage V c The value of the comparison register of the main controller is loaded, the duty cycle of the output drive signal of the main controller is changed, and the switching signal of the switch tube in the switch module of the voltage divider capacitor cascade connected to the negative pole of the power supply is obtained to replace the switching signal generated by the self-excited oscillation unit.

[0029] The advantage of the DC converter control method of the present invention is that voltage balancing of the voltage divider capacitor can be achieved regardless of open-loop mode control or closed-loop mode control; under closed-loop mode control, voltage balancing can be achieved by simply changing the switching signal of the switch tube in the switch module cascaded with the voltage divider capacitor connected to the negative electrode of the power supply, thereby avoiding high-voltage feedback.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention adopts a multi-unit cascade structure to achieve modularization in the true sense. Energy transfer and voltage balancing are achieved between the capacitive voltage dividers (i.e., voltage dividing capacitors) through a non-isolated balancing unit (i.e., balancing unit) without communication and synchronization requirements. The capacitive voltage divider can be superimposed with the corresponding non-isolated balancing unit to expand the input voltage level without considering the drive timing requirements between the non-isolated balancing units. The capacitive voltage divider can be used as an input busbar voltage dividing capacitor to provide energy for the power unit submodule. The number of power unit submodules is independent of the number of capacitive voltage dividers, and the output ends of the power unit submodules can be independent or combined, without considering the risk of input voltage divergence.

[0032] 2. The non-isolated balancing unit of the present invention realizes self-power supply. The non-isolated balancing unit directly draws power from the cascaded capacitor voltage divider without considering the risk of input voltage divergence.

[0033] 3. The non-isolated balancing unit of the present invention is composed of multiple capacitor series-parallel sub-units (i.e., switch modules) and energy storage capacitors between them. Each capacitor series-parallel sub-unit includes at least one switch tube and one diode, which avoids the use of a transformer and greatly simplifies the topology structure and design cost of the converter.

[0034] 4. The control scheme of the present invention is simple and feasible, easily achieving voltage balancing across the capacitor divider regardless of open-loop or closed-loop control. When using closed-loop control, the duty cycle of the power switches within each capacitor series-parallel subunit connected to the negative terminal of the power supply is adjusted based on the total output voltage of the DC converter, thus avoiding high-voltage feedback.

[0035] 5. The non-isolated balancing unit of the present invention can be cascaded and expanded. The non-isolated balancing unit between the capacitive voltage dividers can be cascaded and expanded through multiple capacitor series-parallel sub-units and energy storage capacitors to increase the voltage level of the capacitive voltage divider. The capacitive voltage divider connected to the negative terminal of the input power supply can be cascaded with multiple capacitor series-parallel sub-units and energy storage capacitors. The output of each energy storage capacitor can serve as the input of the power unit submodule, achieving power expansion.

[0036] 6. The power unit submodule (ie, power unit) of the present invention can achieve redundant backup. When a power unit submodule fails and is disconnected or put back into operation, there is no risk of continuous divergence of the input voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The embodiment of the present invention is based on a multi-unit cascade structure and an isolated high-transformation ratio step-down DC converter with power unit submodules output terminals connected in parallel.

[0038] Figure 2 The embodiment of the present invention is based on a multi-unit cascade structure, and the output ends of the power unit submodules are connected in series.

[0039] Figure 3 The invention relates to an isolated high-transformation-ratio step-down DC converter based on a multi-unit cascade structure and with independent output ends of power unit submodules.

[0040] Figure 4 The present invention relates to a non-isolated high-transformation-ratio step-up DC converter based on a multi-unit cascade structure.

[0041] Figure 5 The present invention provides an embodiment of the present invention for implementing power expansion by cascading multiple capacitor series-parallel sub-units and energy storage capacitors through a capacitor voltage divider connected to the negative electrode of the input power supply when performing isolated high-transformation ratio step-down or isolated step-up.

[0042] Figure 6 This is an implementation scheme of a non-isolated balancing unit consisting of two capacitor series-parallel sub-units and a capacitor voltage divider cascade connection.

[0043] Figure 7 This is an implementation scheme of a non-isolated balancing unit consisting of three capacitor series-parallel sub-units and a capacitor voltage divider cascade connection.

[0044] Figure 8 This is an implementation scheme for cascading a non-isolated balancing unit and a capacitor voltage divider, consisting of n (n≥2) capacitor series-parallel sub-units according to an embodiment of the present invention.

[0045] Figure 9 The embodiment of the present invention is a non-isolated balancing unit consisting of n (n≥2) capacitor series-parallel sub-units and a cascade of capacitor voltage dividers. When performing isolated high-ratio step-down or isolated step-up, the power switch tube driving signal and auxiliary power supply implementation plan in each capacitor series-parallel sub-unit are provided.

[0046] Figure 10 The embodiment of the present invention is a non-isolated balancing unit consisting of n (n≥2) capacitor series-parallel sub-units and a cascade capacitor voltage divider. When performing non-isolated high-ratio boosting, the power switch tube driving signal and auxiliary power supply implementation plan in each capacitor series-parallel sub-unit are provided.

[0047] Figure 11 When isolated high-ratio step-down or isolated step-up is performed in the embodiment of the present invention, a capacitive voltage divider connected to the negative pole of the input power supply is cascaded with multiple capacitor series-parallel sub-units and energy storage capacitors to achieve power expansion, a power switch tube drive signal and auxiliary power supply implementation plan is provided.

[0048] Figures 12-15 for Figure 1 The simulation waveform shown is Figure 12 is the total input voltage and total output voltage waveform, Figure 13 The waveforms of the capacitor voltage divider and output voltage when the converter starts are shown in Figure 2. Figure 14 The waveforms of the capacitor voltage divider voltage and output voltage when the second power unit submodule is started are shown in Figure 2. Figure 15 The waveforms of the capacitor voltage divider and the output voltage after the DC converter stabilizes its output. DETAILED DESCRIPTION

[0049] The structure of the DC converter in embodiment 1 of the present invention is as follows: Figure 1 As shown, the DC converter is a modular structure based on a capacitor voltage divider, including multiple non-isolated balancing units (i.e. Figure 1 The balancing unit in the Figure 1The power unit in the circuit). The capacitor voltage dividers are connected in series in sequence, and energy transfer and voltage balancing are performed through a non-isolated balancing unit; the outputs of multiple power unit submodules are connected in parallel to provide the total output of the DC converter, thereby realizing high-ratio isolated step-down. For two adjacent capacitor voltage dividers, the positive input end of each non-isolated balancing unit is connected to the positive pole of the upper-level capacitor voltage divider, the negative input end of each non-isolated balancing unit is connected to the negative pole of the upper-level capacitor voltage divider, the positive output end of each non-isolated balancing unit is connected to the positive pole of the lower-level capacitor voltage divider, and the negative output end of each non-isolated balancing unit is connected to the negative pole of the lower-level capacitor voltage divider. The non-isolated balancing unit is composed of at least two capacitor series-parallel subunits and an energy storage capacitor therebetween. The capacitor series-parallel subunit includes a power switch tube and two diodes. There is an energy storage capacitor between two adjacent capacitor series-parallel subunits. By alternating the power switches of the different capacitor series-parallel subunits within the non-isolated balancing unit, the energy storage capacitors between the different capacitor series-parallel subunits are alternately connected in parallel with the upper and lower capacitor voltage dividers or energy storage capacitors, thereby achieving energy transfer and voltage balancing between the upper and lower capacitor voltage dividers. Each power unit submodule is an isolated DC converter that can convert input voltages within a certain range to the required voltage through internal closed-loop control. Each submodule has a switching switch connected in series at the input.

[0050] The auxiliary power supply of the non-isolated balancing unit is provided by a capacitor voltage divider connected in parallel at its output end. When the self-excited oscillation circuit or the main controller sends a wave through the drive circuit to drive the power switch in the capacitor series-parallel sub-unit to operate, the energy will be transferred from the upper-level capacitor voltage divider to the lower-level capacitor voltage divider, compensating for the voltage drop caused by the auxiliary power supply circuit taking energy from the capacitor voltage divider, and completing energy transfer and voltage balancing at the same time.

[0051] The structure of the DC converter in embodiment 2 of the present invention is as follows: Figure 2 As shown, the difference from Example 1 of the present invention is that the outputs of multiple power unit submodules are connected in series to provide the total output of the DC converter, realizing input series and output series isolated boost. The working principle is the same as that of Example 1 of the present invention and will not be repeated here.

[0052] The structure of the DC converter in embodiment 3 of the present invention is as follows: Figure 3 As shown, the difference from the embodiments 1 and 2 of the present invention is that the output end of one or more power unit submodules is independent and provides the output of the DC converter. The working principle is the same as that of the embodiment 1 of the present invention and will not be repeated here.

[0053] The structure of the DC converter in the fourth embodiment of the present invention is as follows: Figure 4As shown, the difference from embodiments 1, 2, and 3 of the present invention is that the voltage is input only to the capacitor divider connected to the positive terminal of the power supply. All capacitor dividers connected in series directly provide the total output of the DC converter, achieving non-isolated high-ratio boosting. The auxiliary power supply of the non-isolated balancing unit is provided by the capacitor divider connected in parallel to its input. When the self-excited oscillation circuit or the main controller generates a wave and drives the power switch in the capacitor series-parallel sub-unit through the drive circuit, energy is transferred between the capacitor dividers, compensating for the voltage drop caused by the auxiliary power supply circuit drawing energy from the capacitor divider, thereby completing energy transfer and voltage balancing.

[0054] Figures 1 to 4 The embodiment of the non-isolated balancing unit and the capacitor voltage divider cascaded is shown in FIG. Figures 6 to 8 As shown, the non-isolated balancing unit is composed of multiple capacitor series-parallel sub-units and energy storage capacitors in cascade. A capacitor series-parallel sub-unit (i.e., a switch module) includes a power switch tube and two diodes. There is an energy storage capacitor between two adjacent capacitor series-parallel sub-units. Two adjacent capacitor voltage dividers can be cascaded with the non-isolated balancing unit composed of two capacitor series-parallel sub-units and energy storage capacitors ( Figure 6 ), or it can be cascaded with a non-isolated balancing unit consisting of three capacitor series-parallel sub-units and an energy storage capacitor ( Figure 7 ), or it can be cascaded with a non-isolated balancing unit consisting of n (n≥2) capacitor series-parallel sub-units and energy storage capacitors ( Figure 8 ).

[0055] Figure 5 The figure shows an implementation scheme for achieving power expansion by cascading a capacitor voltage divider connected to the negative pole of the input power supply, multiple capacitor series-parallel sub-units, and energy storage capacitors when performing isolated high-ratio buck or isolated boost.

[0056] Figures 5 to 8 The driving signal and auxiliary power supply implementation scheme of the non-isolated balancing unit shown in FIG. Figures 9 to 11 As shown in the figure: When performing isolated high-ratio step-down or isolated boost, the input of the auxiliary power supply of the power switch drive signal in each capacitor series-parallel sub-unit is the output of its corresponding non-isolated balancing unit. As long as the drive signal is sent at least once, energy can be transferred from the upper-level capacitor voltage divider to the lower-level capacitor voltage divider ( Figure 9 ); When performing non-isolated high-ratio boosting, the auxiliary power supply input of the power switch drive signal in each capacitor series-parallel sub-unit is the input of its corresponding non-isolated balancing unit. As long as the drive signal is sent at least once, the energy transfer between the capacitor voltage dividers can be completed ( Figure 10); When performing isolated high-ratio step-down or isolated boost, a capacitor voltage divider connected to the negative pole of the input power supply is cascaded to multiple capacitor series-parallel sub-units and energy storage capacitors, and the input of the auxiliary power supply of the power switch drive signal in each capacitor series-parallel sub-unit is the capacitor voltage divider voltage V connected to the negative pole of the input power supply. Cn ( Figure 11 ), at this time each capacitor C n 、C1#、……、C n-1 #、C n #After the capacitors are connected in parallel and balanced, the voltages of each capacitor will reach a balanced state.

[0057] The working principle of the embodiment of the present invention is described below:

[0058] by Figure 6 For example, the capacitor voltage dividers connected to the previous level non-isolated balancing unit are C1 and C2 respectively. The non-isolated balancing unit is composed of two capacitor series-parallel sub-units. The first capacitor series-parallel sub-unit is composed of S1, D1, and D3, and the second capacitor series-parallel sub-unit is composed of S2, D2, and D4. There is a storage capacitor C1# between the two capacitor series-parallel sub-units. At the same time, D1 acts as a clamping diode to limit the voltage across S1. When S1 is on and S2 is off, C1 and C1# are connected in parallel, and D2 and D3 provide a freewheeling circuit. The upper bus capacitor C1 charges C1#, and C1# stores energy. When S1 is off and S2 is on, C2 and C1# are connected in parallel, and D4 provides a freewheeling circuit. The energy storage capacitor C1# charges C2, and C1# releases energy, thereby realizing energy transfer between upper and lower levels. When both S1 and S2 are off, C1 and C2 are directly connected in series, and C1# does not participate in energy transfer. When both S1 and S2 are on, the upper bus capacitor C1 will be directly short-circuited, damaging the circuit and power devices. Therefore, S1 and S2 cannot be turned on at the same time, and a certain dead time is required. The alternating conduction of S1 and S2 realizes the charging and discharging of C1#, thereby realizing energy transfer and natural balance of capacitor voltage between the upper and lower capacitor voltage dividers C1 and C2. The input of the power unit submodule is connected in parallel with capacitor dividers C1 and / or C2, while the output is connected independently or in series or parallel to provide the total output of the converter. When the power unit submodule is in closed-loop output, it is equivalent to a constant power load connected in parallel across bus capacitors C1 or C2. However, because C1 and C2 achieve energy transfer between the upper and lower capacitor dividers through a non-isolated balancing unit, the capacitor voltages are naturally balanced, avoiding the risk of voltage divergence between the capacitor dividers C1 and C2.

[0059] For the non-isolated balancing unit between the capacitor divider, when there are only two capacitor series-parallel sub-units, Figure 6 For example, D2 and D3 are connected in parallel, and D7 and D6 are connected in parallel. At this time, the two diodes in parallel play the same role, so D2 and D6 can be discarded. Figure 5 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 In the middle, D can be discarded n+x ; Similarly Figure 7 In the middle, D3 and D9 can be discarded. Figures 5 to 11 In the case that there is a margin for the voltage stress of the switch tube in the balancing unit, the clamping diode connected to the source of the switch tube (if the switch tube is a MOSFET) or the emitter of the switch tube (if the switch tube is an IGBT) in each balancing unit can be discarded. The clamping diode plays a clamping role to limit the voltage across the switch tube (considering the influence of parasitic parameters, voltage spikes will be generated, increasing the voltage stress of the switch tube). During the switching process, the balancing current loop is mainly formed by the diode connected to the negative electrode of the energy storage capacitor (non-clamping diode) and the switch tube. When there are n (n>2) capacitor series-parallel sub-units, Figure 8 For example, D2 acts as a clamping diode to limit the voltage across the switch S2.

[0060] The control methods of embodiments 1, 2, 3, and 4 of the present invention are as follows:

[0061] The non-isolated balancing unit can adopt an open-loop or closed-loop operating mode, in which the power switches in each capacitor series-parallel subunit are alternately turned on and a certain dead time is guaranteed. In the closed-loop operating mode, the duty cycle of the power switches in each capacitor series-parallel subunit connected to the negative pole of the power supply is adjusted according to the total output voltage of the DC converter. The specific process is as follows: When the DC converter operates in open-loop mode, the total output voltage is stabilized by the power unit submodule; the switches in all non-isolated balancing units operate at a fixed duty cycle and switching frequency. The switches in a single balancing unit are turned on in sequence, and dead time must be left between them. The switching signal is generated by the self-oscillation unit connected to the balancing unit, and each balancing unit must be connected to a self-oscillation unit. If an isolated high-ratio step-down or isolated boost is performed, the input of each self-oscillation unit is the output of its corresponding non-isolated balancing unit; if a non-isolated high-ratio boost is performed, the input of each self-oscillation unit is the input of its corresponding non-isolated balancing unit. When the DC converter operates in closed-loop mode, the power unit submodule and the capacitor series-parallel subunit connected to the negative pole of the power supply work together to stabilize the total output voltage; the non-isolated balancing unit first operates in open-loop mode, and after the output voltage of each power unit is stabilized, it supplies power to the main controller part; the total output voltage of the DC converter is sampled and conditioned, and the sampled value V o Sent to the main controller, set the output voltage reference value V ref With V o After the difference is controlled by PI, the control voltage V c , by controlling the voltage Vc The value of the comparison register of the main controller is loaded, the duty cycle of the output drive signal of the main controller is changed, and the switching signal of the switch tube in the switch module cascaded with the capacitor voltage divider connected to the negative pole of the power supply is obtained, which replaces the switching signal generated by the self-excited oscillation unit.

[0062] The self-oscillation unit (the self-oscillation unit is a module or chip that can output a PWM drive signal as long as a certain range of input DC voltage is given) is included in Figures 9 to 11 In the driving signal generation part, each balancing unit must be connected to a self-excited oscillation unit ( Figures 9 to 11 Shows the input sources of the auxiliary power supply and drive signal generation parts in different situations).

[0063] When the non-isolated balancing unit of the DC converter operates in open-loop or closed-loop mode, the closed-loop control of the power unit submodule is decoupled from the non-isolated balancing unit, and the number of power unit submodules can be redundantly expanded according to the required output power size, greatly improving the flexibility of the converter in power redundancy expansion.

[0064] When the non-isolated balancing unit of the DC converter operates in closed-loop mode, the main controller part adjusts the duty cycle of the power switch tubes in each capacitor series-parallel sub-unit connected to the negative pole of the power supply by collecting the total output voltage, thereby changing the energy transfer rate of the capacitor voltage divider and avoiding cross-high voltage feedback, which greatly simplifies the hardware circuit design.

[0065] Figures 12 to 15 for Figure 1 The simulation waveform of the DC converter includes 10 non-isolated balancing units and 2 power unit submodules. The simulation parameters are designed as follows:

[0066] Input voltage V in =5000V, line impedance R in =50Ω, line inductance L in =10uH, the number of power unit submodules is 2, and the structure adopts input series and output parallel connection; the number of non-isolated balancing units N = 10, and a non-isolated balancing unit contains two capacitor series-parallel subunits, and there is an energy storage capacitor between the two capacitor series-parallel subunits. Capacitor voltage divider C1 = C2 = ... = C 10=20uF, the energy storage capacitor between the two series-parallel capacitor sub-units is 10uF; connected to the negative pole of the power supply, it does not transfer energy as a voltage divider between the upper and lower capacitors. The non-isolated balancing unit with an independent power unit sub-module at the output end contains two series-parallel capacitor sub-units, and there is an energy storage capacitor between the two series-parallel capacitor sub-units. The energy storage capacitor and the output capacitor are both 10uF. Starting from the positive pole of the input power supply, the frequency of the power switching tubes in the 10 non-isolated balancing units is 50kHz, and the duty cycles are 14.33%, 14.33%, 17.51%, 17.51%, 14.33%, 14.33%, 14.33%, 14.33%, 15.28%, 15.28%, 14.33%, 14.33%, 17.51%, 17.51%, 14.33%, 14.33%, 14.33%. The turn-on times of the two power switches in the same non-isolated balancing unit differ by 10us, with the initial turn-on times being 0us, 10us, 12us, 22us, 24us, 34us, 30us, 40us, 48us, 58us, 60us, 70us, 72us, 82us, 80us, 90us, 96us, 106us, 108us, and 118us, respectively. The power unit submodule uses a single-ended flyback converter based on the UC3844 with closed-loop output voltage control. The operating frequency is f = 20kHz, and the output voltages are set to +5V, +12V, and -12V, respectively. The +5V output terminals of the two power unit submodules are connected in parallel, while the other output terminals are independent. The input ends of the two power unit submodules are connected in parallel with the output ends of the non-isolated balancing unit with independent power unit submodules and the capacitor voltage divider connected to the negative pole of the power supply. The +12V and -12V output ends of the former power unit submodule are both loaded with a size of R L1 =20Ω, the +12V and -12V output terminals of the latter power unit submodule are both loaded with a load of R L2 =80Ω, the load size of the converter +5V output parallel end is R L =0.3Ω, the load power at the converter's +5V output parallel end is 83.33W.

[0067] from Figures 12 to 15The simulation waveforms show that through energy transfer across 10 non-isolated balancing units, and despite inconsistent duty cycles and conduction times of the power switches within each non-isolated balancing unit, and different output powers of the power unit submodules, each capacitor divider voltage achieves voltage balancing. Due to the different power transfer rates, the startup times of the two power unit submodules differ slightly, and the static voltage difference of the capacitor divider increases slightly after the second power unit submodule starts, but this does not cause the capacitor divider voltage to diverge. At the same time, both power unit submodules have power output, and the output voltage meets the closed-loop design requirements, completing a high DC conversion ratio step-down conversion from +5000V to +5V.

Claims

1. A DC converter, characterized in that: include: Multiple voltage-dividing capacitors connected in series; The positive electrode of the i-th voltage-dividing capacitor is connected to the positive input terminal of the i-th balancing unit, and the negative electrode of the i-th voltage-dividing capacitor is connected to the negative input terminal of the i-th balancing unit; The positive output terminal of the i-th balancing unit is connected to the positive electrode of the i+1-th voltage-dividing capacitor, and the negative output terminal of the i-th balancing unit is connected to the negative electrode of the i+1-th voltage-dividing capacitor; The i-th balancing unit is cascaded with the i+1-th balancing unit; The balancing unit includes at least one balancing module; the balancing module includes an energy storage module; the energy storage module is connected in parallel with the input side switch module and the output side switch module; Where, 1≤i≤n-1, n is the number of voltage divider capacitors; The energy storage module is an energy storage capacitor; the input side switch module includes a first switch tube, the first switch tube is connected in series with a first diode, the first diode is connected in parallel with the energy storage capacitor, and a third diode is connected between the anode of the first diode and the negative electrode of the energy storage capacitor; or the input side switch module includes a first switch tube, the first switch tube is connected to the positive electrode of the energy storage capacitor, and the negative electrode of the energy storage capacitor is connected to the third diode; The output side switch module includes a second switch tube, the second switch tube is connected in series with a second diode, the second diode is connected in parallel with the energy storage capacitor, and the anode of the second diode is connected to a fourth diode; or, the output side switch module includes a second switch tube, the positive electrode of the energy storage capacitor is connected to the second switch tube, and the negative electrode of the energy storage capacitor is connected to the fourth diode.

2. The DC converter according to claim 1, wherein: The first to n-1th voltage-dividing capacitors are each connected to at least one power unit; the output ends of all power units are connected in parallel or in series to form the output end of the DC converter; or the output ends of multiple power units correspond to multiple output ends of the DC converter.

3. The DC converter according to claim 2, characterized in that: The first voltage dividing capacitor is connected to the two power units.

4. The DC converter according to claim 2, characterized in that: The power unit is connected to the corresponding voltage-dividing capacitor via a switching switch.

5. The DC converter according to claim 3, characterized in that: The first voltage-dividing capacitor is connected to one of the power units through an output-side balancing unit.

6. The DC converter according to claim 1, characterized in that: The two ends of the branch formed by the multiple voltage-dividing capacitors connected in series are the output ends of the DC converter; the two ends of the nth voltage-dividing capacitor are respectively connected to the positive electrode and the negative electrode of the power supply.

7. The DC converter according to claim 1, characterized in that: When the balancing unit includes a plurality of balancing modules, for two adjacent cascaded balancing modules, the output-side switch module of the first balancing module serves as the input-side switch module of the second balancing module.

8. A control method for a DC converter according to any one of claims 1 to 7, characterized in that: include: Each balancing unit is connected to a self-oscillation unit; In open-loop mode, the switches in all balancing units operate at a fixed duty cycle and switching frequency. Each switch in a single balancing unit is turned on sequentially, with a dead time between the turn-off time of the previous switch and the turn-on time of the next switch. The switching signal is generated by a self-oscillating unit connected to the balancing unit. In the closed-loop mode, the balancing unit first works in the open-loop mode. After the output voltage of each power unit is stable, it supplies power to the main controller. The total output voltage of the DC converter is sampled and conditioned. V o Sent to the main controller to set the output voltage reference value V ref and V o The difference is controlled by PI to obtain the control voltage. V c , by controlling the voltage V c The value of the comparison register of the main controller is loaded, the duty cycle of the output drive signal of the main controller is changed, and the switching signal of the switch tube in the switch module of the voltage divider capacitor cascade connected to the negative pole of the power supply is obtained to replace the switching signal generated by the self-excited oscillation unit.

Images