Isolation type current source converter based on sp type pseudo-hermitian coreless transformer

Abstract

This invention discloses an isolated current source converter based on an SP-type pseudohermite coreless transformer, comprising a negative resistor, an SP-type pseudohermite coreless transformer, a full-bridge rectifier, and a load resistor. The negative resistor is connected to the input terminal of the SP-type pseudohermite coreless transformer. The full-bridge rectifier includes a first rectifier arm, a second rectifier arm, an output filter inductor, and an output filter capacitor. The switching nodes of the first and second rectifier arms are connected to the output terminal of the SP-type pseudohermite coreless transformer. The output filter inductor and output filter capacitor are connected in series and then in parallel with the first and second rectifier arms, respectively. The output filter capacitor is connected in parallel with the load resistor. This invention, using an SP-type pseudohermite coreless transformer as its core, realizes a coreless isolated current source converter with constant current output characteristics independent of the load. This invention achieves corelessness, greatly reducing the weight, size, and cost of the isolated current source converter.

Description

Technical Field

[0001] This invention relates to the technical field of coreless isolated current source converters, and in particular to an isolated current source converter based on an SP-type pseudohermitian coreless transformer. Background Technology

[0002] Traditional isolated current source converters mainly consist of a square wave inverter, a high-frequency transformer, and a rectifier. The high-frequency transformer is the core component of the isolated current source converter, composed of a primary winding, a secondary winding, and a magnetic core. However, the bulky magnetic core of the high-frequency transformer severely limits the lightweight and miniaturized design of isolated current source converters, and hinders further improvements in efficiency and cost reduction. Therefore, coreless isolated current source converters have always been a target for researchers both domestically and internationally, with significant advantages:

[0003] 1. Significantly reduces the weight, size, and cost of isolated current source converters;

[0004] 2. The transformer has no iron loss, further improving the efficiency of the isolated current source converter;

[0005] 3. It avoids the transformer core saturation problem present in traditional isolated current source converters;

[0006] 4. Easier to integrate isolated current source converters.

[0007] Existing advancements in coreless isolated current source converter technology primarily include superconducting coreless isolated current source converters and ultra-high frequency coreless isolated current source converters. However, these coreless isolated current source converters all have significant drawbacks. While superconducting coreless isolated current source converters possess the capability for continuous high-power output, they require operation in extremely low-temperature environments. Even with advanced high-temperature superconducting materials, operation in liquid nitrogen is necessary, making the conditions extremely demanding. They are typically used in applications requiring ultra-high power and where cost is less of a concern. Ultra-high frequency coreless isolated current source converters, while lower in cost and requiring no special operating environment, operate at extremely high frequencies, typically tens of MHz. This necessitates the use of expensive specialized semiconductor switching devices. Furthermore, due to the skin effect and proximity effect, such high switching frequencies result in significant losses, limiting further improvements in output power and efficiency. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings and deficiencies of existing technologies and propose an isolated current source converter based on an SP-type pseudohermitian coreless transformer. Guided by pseudohermitian theory, an SP-type coreless transformer is designed, resulting in an SP-type pseudohermitian coreless transformer with a constant voltage-to-current ratio independent of the load. This achieves high-power, high-efficiency voltage-to-current conversion without using a magnetic core. Using the SP-type pseudohermitian coreless transformer as the core, a coreless isolated current source converter with constant current output characteristics independent of the load is realized. Compared with traditional isolated current source converters, this invention achieves corelessness, greatly reducing the weight, size, and cost of the isolated current source converter. Compared with existing coreless isolated current source converters, it solves the problems of harsh operating environments, high operating costs, high operating frequencies, and high losses.

[0009] To achieve the above objectives, the technical solution provided by this invention is as follows: an isolated current source converter based on an SP-type pseudohermite coreless transformer, comprising a negative resistor, an SP-type pseudohermite coreless transformer, a full-bridge rectifier, and a load resistor; the negative resistor is connected to the input terminal of the SP-type pseudohermite coreless transformer; the SP-type pseudohermite coreless transformer comprises a primary capacitor, a secondary capacitor, a primary winding, and a secondary winding; the primary capacitor and the primary winding are connected in series to form a primary circuit, and the two ends of this primary circuit serve as the input terminals of the SP-type pseudohermite coreless transformer; the secondary capacitor... The primary and secondary coils are connected in series to form a secondary circuit, the two ends of which serve as the output terminals of the SP-type pseudohermitian coreless transformer; there is no core connection between the primary and secondary coils; the full-bridge rectifier includes a first rectifier bridge arm, a second rectifier bridge arm, an output filter inductor, and an output filter capacitor; the switching nodes of the first and second rectifier bridge arms are connected to the output terminals of the SP-type pseudohermitian coreless transformer; the output filter inductor and output filter capacitor are connected in series and then in parallel with the first and second rectifier bridge arms respectively; the output filter capacitor is connected in parallel with the load resistor.

[0010] Furthermore, the primary-side capacitance, secondary-side capacitance, primary-side coil, secondary-side coil, and load resistance of the SP-type pseudohermitian coreless transformer must meet the following pseudohermitian conditions:

[0011]

[0012] In the formula, C1 and C2 are the capacitance values ​​of the primary and secondary sides, respectively, k is the coupling coefficient between the primary and secondary coils, and ω is the operating angular frequency. The resonant frequency of the secondary resonant cavity is . The quality factor of the secondary-side resonant cavity. Let L1 and L2 be the inductance values ​​of the primary and secondary coils, respectively, and R2 = (π / 2) * ... 2 / 8)R L R is the equivalent load resistance. L This is the resistance value of the load resistor.

[0013] Furthermore, the operating angular frequency and the quality factor and coupling coefficient of the secondary resonant cavity satisfy the following relationship:

[0014]

[0015] Furthermore, the output current of the isolated current source converter satisfies the following relationship with the voltage across the negative resistor, the generalized turns ratio, the coupling coefficient, the resonant frequency of the secondary resonant cavity, and the inductance of the secondary coil:

[0016]

[0017] In the formula, V1 is the effective value of the voltage across the negative resistor.

[0018] The working principle of the isolated current source converter based on the SP-type pseudohermitian coreless transformer is as follows: the negative resistor provides energy to the load resistor. When the load resistance changes, the frequency of the output voltage of the negative resistor changes according to the law of equation (2), so that the voltage and current of the negative resistor are in phase (non-associated reference direction), and the power factor is always 1, thereby realizing high-efficiency energy transmission. On this basis, as shown in equation (3), the output current will be independent of the load, exhibiting constant current output characteristics, and realizing the function of the current source converter.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] 1. Compared with traditional isolated current source converters containing magnetic cores, the present invention simplifies the structure of the transformer and eliminates the need for a magnetic core.

[0021] 2. Compared with traditional isolated current source converters containing magnetic cores, the present invention significantly reduces weight, volume and cost, eliminates iron loss, and significantly improves efficiency.

[0022] 3. Compared with existing coreless isolated current source converters, this invention does not require a special working environment and can operate normally at room temperature.

[0023] 4. Compared with existing coreless isolated current source converters, the present invention has a low operating frequency, high output power, and high efficiency, and does not require expensive ultra-high frequency semiconductor switching devices. Attached Figure Description

[0024] Figure 1 This is the circuit schematic diagram of the present invention.

[0025] Figure 2 This is a curve showing the relationship between the operating frequency and the quality factor of the secondary resonant cavity of the present invention.

[0026] Figure 3 This is the curve showing the relationship between output current and output power in this invention.

[0027] Figure 4 This is the efficiency versus output power curve of the present invention.

[0028] Figure 5 This is a typical waveform diagram of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0030] like Figure 1 As shown, this embodiment discloses an isolated current source converter based on an SP-type pseudohermite coreless transformer, including a negative resistor, an SP-type pseudohermite coreless transformer, a full-bridge rectifier, and a load resistor; the negative resistor is connected to the input terminal of the SP-type pseudohermite coreless transformer; the SP-type pseudohermite coreless transformer includes a primary capacitor, a secondary capacitor, a primary winding, and a secondary winding; the primary capacitor and the primary winding are connected in series to form a primary circuit, and the two ends of this primary circuit serve as the input terminals of the SP-type pseudohermite coreless transformer; the secondary capacitor and the secondary winding... The coils are connected in series to form a secondary circuit, and the two ends of this secondary circuit serve as the output terminals of the SP-type pseudohermite coreless transformer. There is no core connection between the primary and secondary coils. The full-bridge rectifier includes a first rectifier bridge arm, a second rectifier bridge arm, an output filter inductor, and an output filter capacitor. The switching nodes of the first and second rectifier bridge arms are connected to the output terminals of the SP-type pseudohermite coreless transformer. The output filter inductor and the output filter capacitor are connected in series and then in parallel with the first and second rectifier bridge arms, respectively. The output filter capacitor is connected in parallel with the load resistor.

[0031] According to Kirchhoff's laws, we can obtain... Figure 1 The system of differential equations shown:

[0032]

[0033] In the formula, L1 and L2 are the inductance values ​​of the primary and secondary coils, respectively; M is the mutual inductance between the primary and secondary coils; C1 is the capacitance value of the primary capacitor; C2 is the converted capacitance value of the secondary capacitor; -R1 is the resistance value of the negative resistor; R2′ is the converted equivalent load resistance value; and q1 and q2 are the charge values ​​of the primary and secondary capacitors, respectively. The conversion relationship between R2′, C2′ and R2, C2 is as follows:

[0034]

[0035] In the formula, ω is the operating angular frequency. The resonant frequency of the secondary resonant cavity is . This is the quality factor of the secondary resonant cavity.

[0036] One of the conditions for constructing a pseudohermitian system is the primary-side resonant cavity frequency. It should be equal to the converted secondary resonant cavity frequency. Let L1 = n 2 If L2,n is the generalized turns ratio, then:

[0037]

[0038] Simplifying equation (4) yields:

[0039]

[0040] In the formula, This is the coupling coefficient between the primary and secondary coils. This is the resonant frequency of the secondary resonant cavity after conversion. This is the quality factor of the secondary resonant cavity after conversion.

[0041] Solving the Lagrange inverse problem for the system represented by equation (7) and applying the Legendre transformation yields the Hamiltonian matrix of the system:

[0042]

[0043] In the formula, X = k 2 -1. Solving for the eigenvalues ​​of the Hamiltonian matrix H yields the system's eigenfrequency, which is the system's operating angular frequency:

[0044]

[0045] The operating frequency f = ω / (2π). Another condition for constructing a pseudohermitian system is that the system's eigenfrequency is a real number. According to equation (9), the eigenfrequency is always a real number when the quality factor Q of the secondary resonant cavity satisfies the following relationship.

[0046]

[0047] In steady state, Figure 1 The voltage v1 across the negative resistor and the primary coil current i L1 Secondary coil current i L2 Secondary capacitor current i C2 Secondary current i R2 Both are sine waves, therefore, according to Kirchhoff's laws, we can obtain...

[0048]

[0049] In the formula, v1 and i respectively L1 i L2 i C2 i R2 The phasor of the secondary current. Substituting equation (9) into equation (11), and letting Q approach 0 to simplify the calculation, the expression for the effective value of the secondary current can be obtained:

[0050]

[0051] The expression for the output current can be derived by utilizing the characteristic that the input power and output power of a full-bridge rectifier are equal.

[0052]

[0053] To demonstrate the accuracy and feasibility of this invention, an isolated current source converter based on an SP-type pseudohermitian coreless transformer was designed and simulated in this embodiment. The effective value of the voltage across the negative resistor is 100V, and the theoretical voltage output current is 3.0A. The designed isolated current source converter based on the SP-type pseudohermitian coreless transformer is as follows: the inductance of the primary coil L1 = 173.6μH, the inductance of the secondary coil L2 = 10.0μH, the coupling coefficient k = 0.5, the capacitance of the primary capacitor C1 = 3.648nF, the capacitance of the secondary capacitor C2 = 63.326nF, and the output filter inductance L... O =220μH, output filter capacitor C O =2.0μF. Considering the total internal resistance of the primary coil and primary capacitor is 30mΩ, the internal resistance of the secondary coil is 10mΩ, and the internal resistance of the secondary capacitor is 5mΩ, simulation was performed using PSIM software. The results are shown below. Figures 2 to 5 As shown.

[0054] Figure 2 The curve showing the relationship between the operating frequency and the quality factor of the secondary resonant cavity demonstrates that the theoretical operating frequency almost matches the simulated operating frequency, proving the correctness of the invention. Figure 3 The curve showing the relationship between output current and output power is shown. From light load to full load, the output current regulation rate does not exceed 5.6%. This regulation rate is caused by the internal resistance of the device, and there is still room for optimization. Figure 4 The curve shows the relationship between efficiency and output power. The peak efficiency is approximately 97.24%, and the efficiency is 95.18% at the maximum output power of 1.5kW, proving that the present invention can achieve efficient energy transmission. Figure 5 The voltage v1 across the negative resistor and the secondary voltage v under full load are the voltage across the negative resistor and the secondary voltage v. R2 Primary coil current i L1 Output current i O From the waveform diagram, we can see v1 and v R2 i L1The waveform is stable and distortion-free. O To stabilize DC power, the ripple is almost negligible, proving that the present invention has good power quality.

[0055] Based on the above analysis, the isolated current source converter based on the SP-type pseudohermitian coreless transformer disclosed in this invention can completely replace the traditional isolated current source converter with a magnetic core and the existing coreless isolated current source converter. The advantages of this invention are obvious and it is worth promoting.

[0056] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An isolated current source converter based on SP type pseudo-hermitian coreless transformer, characterized in that: The system includes a negative resistor, an SP-type pseudohermite coreless transformer, a full-bridge rectifier, and a load resistor. The negative resistor is connected to the input terminal of the SP-type pseudohermite coreless transformer. The SP-type pseudohermite coreless transformer includes a primary capacitor, a secondary capacitor, a primary winding, and a secondary winding. The primary capacitor and the primary winding are connected in series to form a primary circuit, and the two ends of this primary circuit serve as the input terminals of the SP-type pseudohermite coreless transformer. The secondary capacitor and the secondary winding are connected in series to form a secondary circuit. The two ends serve as the output terminals of the SP-type pseudohermitian coreless transformer; there is no core connection between the primary and secondary coils; the full-bridge rectifier includes a first rectifier bridge arm, a second rectifier bridge arm, an output filter inductor, and an output filter capacitor; the switching nodes of the first and second rectifier bridge arms are connected to the output terminals of the SP-type pseudohermitian coreless transformer; the output filter inductor and output filter capacitor are connected in series and then in parallel with the first and second rectifier bridge arms respectively; the output filter capacitor is connected in parallel with the load resistor; The primary capacitance, secondary capacitance, primary winding, secondary winding, and load resistance of the SP-type pseudohermitian coreless transformer must meet the following pseudohermitian conditions: （1）； In the formula, C1 and C2 are the capacitance values of the primary side capacitor and the secondary side capacitor respectively, k is the coupling coefficient between the primary side coil and the secondary side coil, ω is the working angular frequency, ω0 = is the resonance frequency of the secondary side resonance cavity, Q = is the quality factor of the secondary side resonance cavity, n = is the generalized turns ratio, L1 and L2 are the inductance values of the primary side coil and the secondary side coil respectively, R2 =(π 2 / 8)R L is the equivalent load resistance, R L is the resistance value of the load resistance.

2. The isolated current source converter based on an SP-type pseudohermitian coreless transformer according to claim 1, characterized in that: The operating angular frequency and the quality factor and coupling coefficient of the secondary resonant cavity satisfy the following relationship: （2）。 3. The isolated current source converter based on an SP-type pseudohermitian coreless transformer according to claim 2, characterized in that: The output current of the isolated current source converter satisfies the following relationship with the voltage across the negative resistor, the generalized turns ratio, the coupling coefficient, the resonant frequency of the secondary resonant cavity, and the inductance of the secondary coil: （3）； In the formula, V1 is the effective value of the voltage across the negative resistor.

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