A current type energy conversion system

Abstract

The invention discloses a current-type energy conversion system, which comprises a ring-shaped superconducting magnet formed by connecting n arc-shaped magnet modules end to end. Each arc-shaped magnet module is connected in parallel to a DC power grid through a DC bidirectional current source power converter. The power converter controls the voltage and current sharing of each arc-shaped magnet module to generate equal magnetic flux and superimpose it in the arc direction. The power converter adopts a bidirectional current source multi-level topology to reduce device current stress and bus current ripple. A phase shift control strategy is adopted between the power converters to effectively reduce current and total magnetic flux ripple, reduce superconducting magnet AC loss, improve the efficiency of the superconducting system, realize high-efficiency and high-power rapid conversion of electric energy and magnetic energy, and can be applied to energy conversion occasions such as new power grids and integrated power systems for ships.

Description

Technical Field

[0001] The present invention belongs to the field of superconducting application, power electronics, electrical engineering and electric energy new technology, relates to high-efficiency, large-capacity and fast-response superconducting energy storage technology, and specifically relates to a current-type energy conversion system. Background Art

[0002] As a new type of material with excellent electromagnetic properties and great application potential, superconducting materials have the advantages of low conductive loss and high current density. The superconducting magnetic energy storage system can realize the rapid conversion of electrical energy and magnetic energy, achieve millisecond-level power response, and can effectively improve the quality of electric energy and the stability of the power system. The superconducting energy storage system is an energy storage device that uses superconducting magnets to store energy in the power grid in the form of electromagnetic energy, and returns electrical energy to the power grid or for other purposes when needed. It is essentially an inductive energy storage technology, consisting of energy storage magnets, converters, constant temperature dewars, cryogenic refrigeration devices, quench protection devices, monitoring systems, etc.

[0003] The superconducting magnet is the core component of the superconducting magnetic energy storage device, and its stability is related to whether the entire device can operate safely. The superconducting energy storage magnet can be made of high-temperature superconducting materials or low-temperature superconducting materials. The structure of the superconducting magnet can be annular, parallel multi-helical, and single-helical.

[0004] The single-solenoid type has a simple structure and is easy to manufacture, but has a large leakage magnetic field; the parallel multi-solenoid type has a smaller leakage magnetic field, but its energy storage density is very small; the ring-type energy storage magnet uses a medium amount of wire, and the tightly coupled structure constrains the magnetic field inside the ring coil, and the magnet leakage magnetic field is very small. The ring structure is the first choice for large-capacity energy storage magnets, but high power requires the magnet to withstand higher voltages, which poses a challenge to low-temperature thermal insulation.

[0005] The cooling methods and cooling structures of magnets include immersion cooling, steam cooling, and conduction cooling. Conduction cooling does not require cryogenic liquid or steam, but instead conducts the heat of the magnet to the refrigerator through metal cooling materials. It has a compact structure and is easy to maintain. However, the introduction of cooling metal structural parts also brings about problems of low-temperature insulation and eddy current loss, which may limit the power output of the energy storage magnet and reduce the energy storage efficiency.

[0006] On the other hand, due to the existence of pinning centers in high-temperature superconducting materials, when a changing current is applied to the superconductor, the Lorentz force has to overcome the pinning force to do work, generating heat energy, which is called AC loss. AC loss will have an adverse effect on high-temperature superconductors that need to maintain a low-temperature working environment: it will not only increase the cooling cost of superconducting magnets, but also cause the magnet temperature to rise and the critical current to decrease, affecting the performance and stability of high-temperature superconducting magnets.

[0007] Since the DC side energy storage element of superconducting energy storage is an inductor, it is appropriate to adopt a current source converter topology, which can simplify the converter structure and improve the charging / discharging efficiency and safety. In addition to the advantages of the traditional two-level current source converter, the multi-level current source converter also has the advantages of small switching stress of a single device, large output capacity, and small harmonic content of the output waveform. It is particularly suitable for low voltage and high current occasions. In addition, with the development of switching devices with reverse blocking capability (such as integrated gate commutated thyristors), multi-level current source converters have ushered in new opportunities and have good application prospects and development trends. However, the bidirectional multi-level current source converter and its multi-objective coordinated control with modular energy storage magnets increase the technical difficulty of system development, and its development is restricted.

[0008] In principle, superconducting energy storage systems based on high-temperature superconducting materials have the advantages of low operating losses, large working capacity, and small device size. However, in practice, these advantages will be offset by refrigeration costs, and a considerable part of these costs comes from lead losses, mainly including conductive losses and heat leakage losses, which limits their application.

[0009] In summary, the increase in the capacity of superconducting energy storage systems is constrained by the problem that multiple objectives such as efficiency, power, insulation, and cooling of energy storage systems are difficult to be compatible. In particular, the increase in control dimension and the complexity of control strategies have increased the technical difficulty of system development, and its development has been restricted. Analyzing this and seeking solutions is both theoretically meaningful and practically valuable. Summary of the invention

[0010] The purpose of the present invention is to propose a current-type energy conversion system: design a new modular energy storage magnet, reduce the voltage of the unit energy storage magnet, reduce the difficulty of low-temperature insulation design of the conduction cooling magnet, and realize system redundancy and fault tolerance; design a new current source converter, reduce the switching stress of a single device, reduce the output waveform ripple content, reduce AC loss, suitable for low voltage and large current, and realize high efficiency and high power; through the coordinated control of the modular energy storage magnet and the converter, further reduce the output waveform ripple content, reduce AC loss, improve efficiency, and reduce refrigeration requirements; reduce cross-environment leads, fundamentally avoid unnecessary lead losses, and improve the economy of superconducting application technology, so as to realize efficient, safe, stable and rapid operation of a high-power superconducting energy storage system.

[0011] The technical solution adopted by the present invention to solve the technical problem is: a current type energy conversion system adopts superconducting energy storage, comprising a ring-shaped superconducting magnet formed by connecting n unit arc-shaped magnet modules end to end on a circumference, the arc of the arc-shaped magnet module is 2π / n, 2≤n≤10, each arc-shaped magnet module is connected in parallel to the bus of the DC power grid through its own independent DC bidirectional current source power converter, and the charging and discharging current of the arc-shaped magnet module is controlled to be equal to reduce the voltage pressure of the magnet; the power converter controls the equalization of voltage and current of each arc-shaped magnet module, generates equal magnetic flux and superimposes it in the direction of the arc, each power converter has the function of being a backup for each other, and after a unit module circuit fails, the remaining unit modules can continue to operate in fault-tolerant redundancy, thereby improving the reliability of the energy storage system; the power converter adopts an M-level topology, 2≤m≤9, reduces the device current stress, reduces the bus current ripple, the bridge arm number i∈{1,...,m-1}, j∈{1,...,m-1}, the power switch tube T ei The emitter of the diode D ei The negative electrodes are connected in series, marked as connection point E i , forming the bridge arm Q ei , E i With connection point E i+1 Connect the shunt inductor L between ei , power switch tube T fj The collector of the diode D fj The positive electrodes are connected in series, marked as the connection point F j , forming the bridge arm Q fj , F j With connection point F j+1 Connect the shunt inductor L between fj , connection points E1 and F1 are connected to the two ends of the arc magnet module respectively, and the bridge arm Q ei With bridge arm Q fj Connected in parallel to the DC bus support capacitor C, the DC bus supports the capacitor C in parallel, and the bridge arm Q ei Upper power switch tube T ei The collector is connected to the positive bus P, and the bridge arm Q ei Upper diode D ei The positive pole is connected to the negative busbar N, and the bridge arm Q fj Upper power switch tube T fj The emitter is connected to the negative bus N, and the bridge arm Q fj Upper diode D fj The negative pole is connected to the positive bus P, and each shunt inductor L ei The current values ​​are not equal, and the shunt inductance L fj The current values ​​are not equal.

[0012] Furthermore, the arc magnet module is mainly composed of a superconducting coil, an inner ring, an outer ring, a radial support assembly, a cooling plate, a supporting side plate, a current lead assembly and a low-temperature glue.

[0013] Furthermore, the M-level power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnetic module: the power switch tube T ei Drive pulse trigger, power switch tube T ei Turn on, power switch tube T fj Drive pulse trigger, power switch tube T fj Turn on, the arc magnet module is charged; the power switch tube T ei Drive pulse trigger, power switch tube T ei Turn on, power switch tube T fj Drive pulse blocked, power switch tube T fj Blocking, diode D ei Blocking, diode D fj Turn on, arc magnet module continues current; power switch tube T ei Drive pulse blocked, power switch tube T ei Blocking, power switch tube T fj Drive pulse trigger, power switch tube T fj Conducting, diode D ei Conducting, diode D fj Blocking, arc magnet module continuous current; power switch tube T ei Drive pulse blocked, power switch tube T ei Blocking, power switch tube T fj Drive pulse blocked, power switch tube T fj Blocking, diode D ei 、Diode D fj Turn on, the arc magnet module discharges.

[0014] Furthermore, the arc magnet module current adopts closed-loop control, and the regulator realizes fast tracking and error-free regulation of the charge and discharge current, and maintains the current balance of each module: The reference instruction is used to output the absolute value of the signal through the PI current regulator as the common reference modulation wave of each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

[0015] In the current-type energy conversion system, a multi-level carrier stacking pulse width modulation strategy is adopted for the power switch tube. By comparing the carrier wave and the modulation wave, a switch pulse width control signal is obtained to control the switch tube to be turned on and off. According to the different arrangements of the phase relationship between the triangular carrier waves, three carrier stacking PWM modes are selected: (1) an in-phase stacking mode, in which all carrier waves are arranged and stacked up and down with the same phase; (2) a positive and negative anti-phase stacking mode, in which the phase of the carrier wave above the zero value is opposite to the phase of the carrier wave below the zero value; and (3) an alternating reverse stacking mode, in which the phases of all adjacent carrier waves are opposite.

[0016] In the current-type energy conversion system, the power switch tube adopts a multi-level carrier phase-shift pulse width modulation strategy, and generates a PWM wave to control each group of power units respectively by comparing a plurality of triangular carriers with the same amplitude and phase shift, and then superimposes them to form a multi-level PWM waveform.

[0017] In the current-type energy conversion system, each power converter, i.e., power converter Ck, k∈{1, ..., n}, adopts a phase shift control strategy, which effectively reduces the total magnet synthetic flux ripple, reduces the arc magnet module induced potential and current ripple, and reduces the superconducting magnet AC loss; reduces the bus current ripple, and the power converters C1, C n Each cluster triggers a pulse sequence, shifting the phase by 2π / n within a switching cycle T. The converter modules C1 and C n Each cluster of trigger pulse sequences is delayed by T / n in sequence.

[0018] Furthermore, the power switch tube T i , T j It is a reverse-resistance switching device with reverse blocking capability but no reverse conducting capability; or it is a reverse-conducting switching device with reverse conducting capability and a diode connected in series in the forward direction at the emitter.

[0019] Furthermore, the switching device may be one of a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT, and a metal oxide semiconductor field effect transistor MOSFET.

[0020] The beneficial effects of the present invention are as follows: the present invention adopts a combination of multiple arc-shaped magnet modules to form an annular superconducting magnet, each arc-shaped magnet module is connected in parallel to the DC power grid through its own independent power converter, reducing voltage stress; the power converter adopts a bidirectional current source multi-level topology, reducing device current stress and bus current ripple, and a phase shift control strategy is adopted between each power converter, effectively reducing current and total magnetic flux ripple, and reducing superconducting magnet AC loss; the converter current sharing / shunting inductor adopts superconducting materials, reducing losses and improving the efficiency of the superconducting system. The annular superconducting magnet can realize the rapid conversion of high-efficiency and high-power electric energy and magnetic energy, and can be applied to energy conversion occasions such as new power grids and integrated ship power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 It is a schematic structural diagram of a power converter of the present invention; Figure 3 Schematic diagram of three traditional superconducting magnet structures; Figure 4 It is a schematic structural diagram of the annular superconducting magnet of the present invention; Figure 5 It is a partial cross-sectional view of the annular superconducting magnet of the present invention; Figure 6 is an exploded schematic diagram of the arc magnet module; Figure 7 It is a schematic diagram of the structure of the arc-shaped magnet module cooling plate and supporting side plate; Figure 8 It is a topological structure diagram of a DC bidirectional current source power converter; Fig. 9 and Fig.10 is a schematic diagram of the switch device structure; Fig.11 The switching mode of the M-level topology power converter of the present invention; Fig.12 It is the closed-loop control strategy of the present invention; Fig.13 It is a bidirectional current source multi-level topology carrier in-phase stacked modulation; Fig.14 It is a bidirectional current source multi-level topology with positive and negative reverse phase stacked modulation; Fig.15 It is a bidirectional current source multi-level topology with alternating reverse stacked modulation; Fig.16 It is a bidirectional current source multi-level topology carrier phase shift modulation PWM modulation waveform; Fig.17 The switching state and inductor current waveform of the bidirectional current source multi-level topology carrier phase shift modulation; Fig.18 The current waveform adopts phase shift control strategy between arc magnet modules.

[0022] The reference numerals of the figures are: 01 - superconducting coil, 02 - inner ring, 03 - outer ring, 04 - radial support assembly, 05 - cooling plate, 06 - support side plate, 07 - current lead assembly. DETAILED DESCRIPTION

[0023] The present invention is further described in detail with reference to the accompanying drawings and embodiments as follows.

[0024] Reference Figure 1 As shown, the present invention discloses a current-type energy conversion system, which uses superconducting energy storage. The system uses n arc-shaped magnet modules, 2≤n≤10, and each arc-shaped magnet module has a radian of 2π / n. They are combined on the circumference to form a circular magnet as a whole. The tightly coupled structure constrains the magnetic field inside the circular coil, and the magnetic leakage field is very small. Each arc-shaped magnet module is connected in parallel to the busbar of the DC power grid through its own independent DC bidirectional current source power converter. The arc-shaped magnet module controls each arc-shaped magnet module to balance voltage and current, generate equal magnetic flux, and superimpose in the arc direction, such as Figure 2 shown.

[0025] The structure of conventional superconducting magnets is Figure 3 As shown in the figure, a is a single solenoid, b is a multi (quadruple) solenoid, and c is a ring magnet. Different from the traditional superconducting magnet structure, the arc of the arc magnet module of the present invention is 2π / n, 2≤n≤10, as shown in the figure. Figure 4 and Figure 5 As shown in the figure, the tightly coupled structure constrains the magnetic field inside the toroidal coil, and the magnetic leakage field is very small; the power converter controls the voltage and current of each arc-shaped magnet module, generates equal magnetic flux and superimposes it in the arc direction, and each power converter has the function of mutual backup. After a unit module circuit fails, the remaining unit modules can continue to operate with fault tolerance and redundancy, which improves the reliability of the energy storage system. The converter shunt inductor is made of superconducting material and is integrated with the superconducting magnet into a cryostat dewar, reducing lead loss.

[0026] Reference Figure 6 As shown, the arc magnet module is mainly composed of a superconducting coil 01, an inner ring 02, an outer ring 03, a radial support assembly 04, a cold plate 05, a support side plate 06, a current lead assembly 07 and a low-temperature glue. The structure of the cold plate 05 and the support side plate 06 is as shown in FIG. Figure 7 shown.

[0027] DC bidirectional current source power converter Figure 8The power converter adopts M-level topology, 2≤m≤9, which reduces the device current stress and bus current ripple. The bridge arm number i∈{1,…,m-1}, j∈{1,…,m-1}, and the power switch tube T ei The emitter of the diode D ei The negative electrodes are connected in series, marked as connection point E i , forming the bridge arm Q ei , E i With connection point E i+1 Connect the shunt inductor L between ei , power switch tube T fj The collector of the diode D fj The positive electrodes are connected in series, marked as the connection point F j , forming the bridge arm Q fj , F j With connection point F j+1 Connect the shunt inductor L between fj , connection points E1 and F1 are connected to the two ends of the arc magnet module respectively, and the bridge arm Q ei With bridge arm Q fj Connected in parallel to the DC bus support capacitor C, the DC bus supports the capacitor C in parallel, and the bridge arm Q ei Upper power switch tube T ei The collector is connected to the positive bus P, and the bridge arm Q ei Upper diode D ei The positive pole is connected to the negative busbar N, and the bridge arm Q fj Upper power switch tube T fj The emitter is connected to the negative bus N, and the bridge arm Q fj Upper diode D fj The negative pole is connected to the positive bus P, and each shunt inductor L ei The current values ​​are not equal, and the shunt inductance L fj The current values ​​are not equal.

[0028] The power switch tube T i , T j It is a reverse blocking type switching device with reverse blocking capability but no reverse conducting capability; or it is a reverse conducting type switching device with reverse conducting capability with a diode connected in series in the forward direction of the emitter. The switching device can be a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT, a metal oxide semiconductor field effect transistor MOSFET, such as Fig. 9 and Fig.10 shown.

[0029] The M-level power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnet module. The switch table of the M-level power converter is as follows: Fig.11 shown.

[0030] Power switch tube T ei Drive pulse trigger, power switch tube T ei Turn on, power switch tube T fj Drive pulse trigger, power switch tube T fj Turn on, the arc magnet module is charged.

[0031] Power switch tube T ei Drive pulse trigger, power switch tube T ei Turn on, power switch tube T fj Drive pulse blocked, power switch tube T fj Blocking, diode D ei Blocking, diode D fj Turn on, the arc magnet module continues current.

[0032] Power switch tube T ei Drive pulse blocked, power switch tube T ei Blocking, power switch tube T fj Drive pulse trigger, power switch tube T fj Conducting, diode D ei Conducting, diode D fj Blocked, arc magnet module continues current.

[0033] Power switch tube T ei Drive pulse blocked, power switch tube T ei Blocking, power switch tube T fj Drive pulse blocked, power switch tube T fj Blocking, diode D ei 、Diode D fj The arc magnet module is turned on and discharged.

[0034] The arc magnet module current is controlled by closed loop, such as Fig.12 As shown in the figure, the regulator can achieve fast tracking and error-free regulation of charge and discharge currents, and maintain current balance in each module: The reference instruction is used to output the absolute value of the signal through the PI current regulator as the common reference modulation wave of each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

[0035] The power switch tube adopts a multi-level carrier stacking pulse width modulation strategy. By comparing the carrier and the modulation wave, the switch pulse width control signal is obtained to control the switch tube to be turned on and off. According to the different arrangements of the phase relationship between the triangular carriers, three carrier stacking PWM methods are selected: (1) In-phase stacking method, all carriers are arranged up and down with the same phase, such as Fig.13As shown; (2) The positive and negative anti-phase stacking makes the carrier phase above zero value and the carrier phase below zero value opposite, as shown Fig.14 As shown; (3) Alternating reverse stacking, which means that the phases of all adjacent carriers are opposite, such as Fig.15 shown.

[0036] The power switch tube adopts a multi-level carrier phase-shift pulse width modulation strategy. By comparing multiple triangular carriers with the same amplitude and phase shift with the modulation wave, a PWM wave is generated to control each group of power units respectively, and then superimposed to form a multi-level PWM waveform, such as Fig.16 The carrier phase shift method has the advantage of modularity.

[0037] The carrier phase shift method has become the standard PWM control method for H-bridge multi-level circuits. Compared with other PWM control methods, it has the following advantages: (1) It guarantees the same output voltage and switching frequency at any modulation ratio (at any frequency). When the modulation ratio of other carrier methods is reduced, some unit bridges will have no PWM voltage output, causing the switching frequency of the output current to decrease and the harmonic content of the output current to increase; (2) There is no problem of output power imbalance between unit bridges. Because in the PS method, the PWM waveform of the output voltage between each level is basically the same. Other methods will be inconsistent, resulting in different powers of unit bridges at different levels; (3) Consistent with the modular structure of the main circuit, the carrier and modulation wave for each unit in the PS carrier comparison PWM method also present a modular structure; (4) For the same carrier frequency, the frequency of the output current of the PS method is m times the carrier frequency.

[0038] The trigger pulse sequences of each cluster of power converters C1 and Cn are phase-shifted by 2π / n within a switching cycle T, and the trigger pulse sequences of each cluster of converter modules C1 and Cn are sequentially delayed by T / n, such as Fig.17 shown.

[0039] The phase shift control strategy is adopted between each power converter, that is, the power converter Ck, k∈{1,…,n} effectively reduces the total magnet synthetic flux ripple, reduces the magnet module induced potential and current ripple, reduces the superconducting magnet AC loss; reduces the bus current ripple, and the current waveform is as follows Fig.18 shown.

[0040] The invention adopts a pulse synchronization control strategy between the arc-shaped magnet modules to ensure the current balance of the magnet modules; the converter shunt inductor adopts superconducting material to reduce the loss of the shunt inductor.

[0041] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many modifications without departing from the scope of protection of the present invention and the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A current-type energy conversion system, characterized in that: The invention comprises a ring-shaped superconducting magnet formed by connecting n arc-shaped magnet modules end to end, wherein the arc of the arc-shaped magnet module is 2π / n, 2≤n≤10, each arc-shaped magnet module is connected in parallel to the busbar of the DC power grid through a DC bidirectional current source power converter, and the power converter controls the voltage and current balancing of each arc-shaped magnet module to generate equal magnetic flux and superimpose in the arc direction; the power converter adopts an M-level topology, 2≤m≤9, and the power switch tube T ei The emitter of the diode D ei The negative electrodes are connected in series, and the connection point is E i , forming the bridge arm Q ei , E i With connection point E i+1 Connect the shunt inductor L between ei , power switch tube T fj The collector of the diode D fj The positive electrodes are connected in series, and the connection point is F j , forming the bridge arm Q fj , F j With connection point F j+1 Connect the shunt inductor L between fj , connection points E1 and F1 are connected to the two ends of the arc magnet module respectively, and the bridge arm Q ei With bridge arm Q fj Connected in parallel to the DC bus support capacitor C, the power switch tube T ei The collector of diode D is connected to the positive bus. ei The positive pole is connected to the negative bus, and the power switch tube T fj The emitter of diode D is connected to the negative bus. fj The negative pole is connected to the positive bus.

2. A current-source energy conversion system according to claim 1, characterized in that: The arc-shaped magnet module is obtained by assembling a superconducting coil (01), an inner ring (02), an outer ring (03), a radial support assembly (04), a cooling plate (05), a support side plate (06) and a current lead assembly (07) with low-temperature glue, followed by vacuum impregnation filling and curing at room temperature.

3. A current-source energy conversion system according to claim 1 or 2, characterized in that: The M-level power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnetic module: the power switch tube T ei Drive pulse trigger, power switch tube T ei Turn on, power switch tube T fj Drive pulse trigger, power switch tube T fj Turn on, the arc magnet module is charged; the power switch tube T ei Drive pulse trigger, power switch tube T ei Turn on, power switch tube T fj Drive pulse blocked, power switch tube T fj Blocking, diode D ei Blocking, diode D fj Turn on, arc magnet module continues current; power switch tube T ei Drive pulse blocked, power switch tube T ei Blocking, power switch tube T fj Drive pulse trigger, power switch tube T fj Conducting, diode D ei Conducting, diode D fj Blocking, arc magnet module continuous current; power switch tube T ei Drive pulse blocked, power switch tube T ei Blocking, power switch tube T fj Drive pulse blocked, power switch tube T fj Blocking, diode D ei 、Diode D fj Turn on, the arc magnet module discharges.

4. A current-source energy conversion system according to claim 3, characterized in that: The arc magnet module current adopts closed-loop control, and the regulator realizes fast tracking and error-free regulation of the charge and discharge current, and maintains the current balance of each module: The reference instruction is used to output the absolute value of the signal through the PI current regulator as the common reference modulation wave of each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

5. A current-source energy conversion system according to claim 4, characterized in that: The power switch tube adopts a multi-level carrier stacking pulse width modulation strategy. By comparing the carrier and the modulation wave, the switch pulse width control signal is obtained to control the on and off of the switch tube. According to the different arrangements of the phase relationship between the triangular carriers, the following are selected: (1) in-phase stacking method, all carriers are arranged up and down with the same phase; (2) positive and negative anti-phase stacking method makes the phase of the carrier above zero value and the phase of the carrier below zero value opposite; (3) alternating reverse stacking method, which means that the phases of all adjacent carriers are opposite.

6. A current-source energy conversion system according to claim 4, characterized in that: The power switch tube adopts a multi-level carrier phase-shift pulse width modulation strategy. By comparing multiple triangular carriers with the same amplitude and phase shift, the modulated wave is generated to control each group of power units respectively, and then superimposed to form a multi-level PWM waveform.

7. A current-source energy conversion system according to claim 6, characterized in that: The power converters Ck, k∈{1,…,n} adopt a phase shift control strategy. n Each cluster triggers a pulse sequence, shifting the phase by 2π / n within a switching cycle T. The converter modules C1 and C n Each cluster of trigger pulse sequences is delayed by T / n in sequence.

8. A current-source energy conversion system according to claim 7, characterized in that: The power switch tube is a reverse-resistance switch device with reverse blocking capability but no reverse conducting capability; or a reverse-conducting switch device with reverse conducting capability with a diode connected in series in the forward direction at the emitter.

9. A current-source energy conversion system according to claim 7, characterized in that: The switch device is a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT or a metal oxide semiconductor field effect transistor MOSFET.

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