A new energy grid-connected detection platform adjustable reactance control method

Abstract

This invention relates to an adjustable reactor control method for a new energy grid-connected testing platform, belonging to the field of adjustable reactor technology. The method includes five main steps: defining a switching function, calculating the voltage value of the secondary winding, calculating the voltage and current values ​​of the primary winding, calculating the impedance of the primary winding, and linearly adjusting the reactor. This invention changes the impedance of the adjustable reactor by altering the duty cycle. When the duty cycle is increased, the magnitude of the adjustable reactor's impedance decreases; when it is decreased, the impedance of the adjustable reactor increases. In other words, this invention can linearly adjust the reactance, has a simple structure, and is easy to implement in engineering.

Description

Technical Field

[0001] This invention belongs to the field of adjustable reactance control technology, specifically relating to an adjustable reactance control method for a new energy grid-connected detection platform. Background Technology

[0002] As a key sector for achieving the dual goals of "carbon peaking and carbon neutrality," the power industry prioritizes promoting a low-carbon energy transition and establishing a new power system dominated by green energy. Wind and solar power will become important sources of electricity supply. However, with the increasing penetration rate of new energy sources and the proportion of power electronic equipment in the system, the power grid is gradually shifting from a synchronous machine-dominated system to a converter-dominated system. The reduction in system inertia, the significant decrease in the short-circuit ratio at the common coupling point, and the substantial increase in grid impedance due to long-distance transmission lines and multi-stage transformer voltage boosting all contribute to the characteristics of a weak or even extremely weak power grid. Therefore, the power grid places higher demands on the integration of new energy sources and power electronic equipment. To simulate the response characteristics of new energy grid connection under external grid faults, the application of a new energy grid connection detection platform that simulates different grid fault states is of great significance.

[0003] Adjustable reactors, as a fundamental device in new energy grid-connected testing platforms, play a crucial role in the system's stability and safety. Furthermore, many problems related to harmonic suppression, overvoltage, and overcurrent limiting can be addressed using adjustable impedance; therefore, new energy grid-connected testing platforms should possess linearly adjustable reactor functionality. However, currently, it is difficult to precisely control the mechanics of traditional adjustable-turn reactors, thus preventing continuous adjustment.

[0004] Chinese invention patent application CN118017531A, published on May 10, 2024, discloses an adjustable reactance control method. This method employs controllable devices to adjust the primary-side reactance winding by controlling the switching of thyristors and the output current of transistors, thereby achieving arbitrary impedance adjustment. Thyristor switching control enables coarse adjustment of the adjustable reactance, while transistor output current control enables fine adjustment. Although this method can perform coarse and fine adjustments to the adjustable reactor, it requires a large number of components, resulting in high cost, large size, and complex control, making its implementation difficult in new energy grid-connected testing platforms.

[0005] Chinese invention patent CN117912820A, published on April 19, 2024, discloses a PWM-type series resonant adjustable reactor and its control method for vector testing. This method utilizes an adjustable capacitor and an adjustable inductor under PWM chopping control to form a series resonant circuit, thus compressing the size of the adjustable reactor. Furthermore, the adjustable reactor topology provides a freewheeling loop. Under high-frequency PWM control, the sinusoidal current output of the adjustable reactor has low harmonic content and will not affect the system under test, solving the technical problem of high-frequency harmonic coupling in PWM chopping control. While this method offers continuously adjustable reactance and reduces size, it requires multiple IGBTs and MOSFETs, making the control system relatively complex.

[0006] Therefore, overcoming the shortcomings of existing technologies is a problem that urgently needs to be solved in the field of adjustable reactance control technology. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide an adjustable reactance control method for a new energy grid-connected testing platform, so as to achieve linear adjustment of the reactance of the new energy grid-connected testing platform.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for controlling adjustable reactors in a new energy grid-connected testing platform, wherein the new energy grid-connected testing platform includes a rectifier unit, a DC power supply, an inverter unit, adjustable reactors, and a transformer;

[0010] The three-phase input voltage is connected to the DC power supply through the rectifier unit, the DC power supply is connected to the DC side of the inverter unit, and the AC side of the inverter unit is output through the adjustable reactor and then connected to the device under test through the transformer.

[0011] The adjustable reactance includes an S1 transistor, an S2 transistor, a primary winding, and a secondary winding. Both the S1 and S2 transistors are composed of an IGBT and an anti-parallel diode, and are connected in series in reverse in the circuit. The emitter of the S1 IGBT is connected to the emitter of the S2 IGBT. The collectors of the two IGBTs are connected to the two ends of the secondary winding. The gates of the S1 and S2 IGBTs are respectively connected to a PWM generator.

[0012] The adjustable reactor control method for the new energy grid-connected testing platform includes the following steps:

[0013] Step (1): Define a switching function f to control the IGBTs of transistors S1 and S2 to turn on and off, with the IGBTs of transistors S1 and S2 conducting complementaryly.

[0014]

[0015] Perform a Fourier expansion on f:

[0016]

[0017] In the formula, α is the duty cycle of the IGBT, k is the ratio of the secondary winding voltage period to the PWM wave period, F(α, k) is the Fourier expansion term; n is an integer in [1,∞], ω is the angular frequency, and t is time;

[0018] F(α,k)=sin(nωτ)+sin[nω(T c +τ)]-sinnωT c +sin[nω(2T c +τ)]

[0019] In the formula, τ is the conduction time in the PWM wave, ω is the voltage angular frequency, and T c The period of the PWM wave;

[0020] Step (2): When the IGBT is turned on and off using PWM wave control, S1 and S2 are turned on alternately and complementaryly. The actual voltage value of the secondary winding is calculated through step (1). Ignoring higher harmonics and considering only the fundamental wave, we get:

[0021] u2=fU N sinωt=αU N sinωt

[0022] In the formula, u2 is the actual voltage of the secondary winding, U N Given the rated voltage of the secondary winding and the impedance value of the secondary winding, Z2, the current value of the secondary winding, i2, is obtained:

[0023]

[0024] Step (3): Based on the current of the secondary winding obtained in step (2), and assuming the turns ratio of the primary winding to the secondary winding is N, the voltage U of the primary winding is obtained. N1 The current value i1 of the primary winding;

[0025] Step (4): Obtain the voltage U of the primary winding according to step (3). N1 Given the current value i1 of the primary winding, the impedance Z1 of the primary winding is calculated.

[0026] Step (5): Based on the results obtained in step (4), pulses with different duty cycles are sent through the PWM generator. By changing the conduction and cutoff of transistors S1 and S2, the current of the secondary winding of the adjustable reactor is changed. The reverse magnetic flux generated changes the core reluctance of the adjustable reactor, thereby realizing continuous adjustment of the inductance value.

[0027] Furthermore, preferably, the inverter unit is a DC / AC inverter unit.

[0028] Furthermore, preferably, the transformer is an isolation step-up transformer.

[0029] Furthermore, preferably, the equipment under test is a wind turbine, a photovoltaic system, or an energy storage device.

[0030] Furthermore, preferably, in step (3), the voltage U of the primary winding is... N1 The formula for calculating the current value i1 of the primary winding is as follows:

[0031]

[0032] Therefore, the primary winding current is obtained as follows:

[0033]

[0034] Furthermore, preferably, in step (4), the impedance Z1 of the primary winding is calculated using the following formula:

[0035]

[0036] This invention allows the impedance of an adjustable reactor to be changed by altering the duty cycle α. When α increases, the magnitude of the adjustable reactor's impedance decreases; when α decreases, the impedance of the adjustable reactor increases.

[0037] In this invention, when the S1 IGBT is fully turned on, the current in the secondary winding is at its maximum, which in turn maximizes the current in the primary winding, thus reducing the resistance of the adjustable reactor. Similarly, when the S1 IGBT is fully turned off, the secondary winding is essentially open-circuited with no current generated, and the current in the primary winding reaches its minimum value. At this time, the resistance of the adjustable reactor reaches its maximum. By changing the duty cycle of the IGBT, the adjustable reactor can be continuously adjusted within the power supply cycle, which is the core technology of this invention.

[0038] Compared with the prior art, the beneficial effects of this invention are as follows:

[0039] This invention provides an adjustable reactance control method for a new energy grid-connected monitoring platform. This method can linearly adjust the reactance, has a simple structure, and is easy to implement in engineering. It uses IGBT transistors, which are small, high-frequency switching devices with fast response speeds. Only a small LC filter is needed to remove high-order harmonics, reducing harmonic pollution. Figure 3 The simulation model of the adjustable reactor in the new energy grid-connected testing platform shown in Table 1 can obtain impedance data under different duty cycles.

[0040] Table 1 Simulation data under different duty cycles

[0041] PWM duty cycle α <![CDATA[Primary winding voltage U N1 > <![CDATA[Primary winding current i1]]> <![CDATA[Adjustable reactor impedance Z1]]> 0 193.0V 0.054A 3574.07Ω 0.2 190.7V 0.065A 2933.85Ω 0.5 170.2V 0.167A 1019.16Ω 0.8 146.1V 0.288A 507.29Ω 1 88.38V 0.577A 153.17Ω

[0042] As can be seen from Table 1, as the duty cycle of the PWM wave increases, the primary winding voltage of the adjustable reactor decreases, the primary winding current increases with the increase of the duty cycle, and the primary winding impedance of the adjustable reactor decreases with the increase of the duty cycle, thus realizing the linear adjustability of the adjustable reactor. Attached Figure Description

[0043] Figure 1 Topology diagram of the new energy grid connection testing platform;

[0044] Figure 2 Control principle diagram of the adjustable reactor for a new energy grid connection testing platform;

[0045] Figure 3 This is a simulation diagram of an adjustable reactor for a new energy grid connection testing platform. Detailed Implementation

[0046] The present invention will now be described in further detail with reference to the embodiments.

[0047] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the field or according to the product instructions. Materials or equipment whose manufacturers are not specified are all conventional products that can be obtained by purchase.

[0048] Example 1

[0049] A method for controlling adjustable reactors in a new energy grid-connected testing platform, wherein the new energy grid-connected testing platform includes a rectifier unit, a DC power supply, an inverter unit, adjustable reactors, and a transformer;

[0050] The three-phase input voltage is connected to the DC power supply through the rectifier unit, the DC power supply is connected to the DC side of the inverter unit, and the AC side of the inverter unit is output through the adjustable reactor and then connected to the device under test through the transformer.

[0051] The adjustable reactance includes an S1 transistor, an S2 transistor, a primary winding, and a secondary winding. Both the S1 and S2 transistors are composed of an IGBT and an anti-parallel diode, and are connected in series in reverse in the circuit. The emitter of the S1 IGBT is connected to the emitter of the S2 IGBT. The collectors of the two IGBTs are connected to the two ends of the secondary winding. The gates of the S1 and S2 IGBTs are respectively connected to a PWM generator.

[0052] The adjustable reactor control method for the new energy grid-connected testing platform includes the following steps:

[0053] Step (1): Define a switching function f to control the IGBTs of transistors S1 and S2 to turn on and off, with the IGBTs of transistors S1 and S2 conducting complementaryly.

[0054]

[0055] Perform a Fourier expansion on f:

[0056]

[0057] In the formula, α is the duty cycle of the IGBT, k is the ratio of the secondary winding voltage period to the PWM wave period, F(α, k) is the Fourier expansion term; n is an integer in [1,∞], ω is the angular frequency, and t is time;

[0058] F(α,k)=sin(nωτ)+sin[nω(T c +τ)]-sinnωT c +sin[nω(2T c +τ)]

[0059] In the formula, τ is the conduction time in the PWM wave, ω is the voltage angular frequency, and T c The period of the PWM wave;

[0060] Step (2): When the IGBT is turned on and off using PWM wave control, S1 and S2 are turned on alternately and complementaryly. The actual voltage value of the secondary winding is calculated through step (1). Ignoring higher harmonics and considering only the fundamental wave, we get:

[0061] u2=fU N sinωt=αU N sinωt

[0062] In the formula, u2 is the actual voltage of the secondary winding, U N Given the rated voltage of the secondary winding and the impedance value of the secondary winding, Z2, the current value of the secondary winding, i2, is obtained:

[0063]

[0064] Step (3): Based on the current of the secondary winding obtained in step (2), and assuming the turns ratio of the primary winding to the secondary winding is N, the voltage U of the primary winding is obtained. N1 The current value i1 of the primary winding;

[0065] Step (4): Obtain the voltage U of the primary winding according to step (3). N1 Given the current value i1 of the primary winding, the impedance Z1 of the primary winding is calculated.

[0066] Step (5): Based on the results obtained in step (4), pulses with different duty cycles are sent through the PWM generator. By changing the conduction and cutoff of transistors S1 and S2, the current of the secondary winding of the adjustable reactor is changed. The reverse magnetic flux generated changes the core reluctance of the adjustable reactor, thereby realizing continuous adjustment of the inductance value.

[0067] Example 2

[0068] A method for controlling adjustable reactors in a new energy grid-connected testing platform, wherein the new energy grid-connected testing platform includes a rectifier unit, a DC power supply, an inverter unit, adjustable reactors, and a transformer;

[0069] The three-phase input voltage is connected to the DC power supply through the rectifier unit, the DC power supply is connected to the DC side of the inverter unit, and the AC side of the inverter unit is output through the adjustable reactor and then connected to the device under test through the transformer.

[0070] The adjustable reactance includes an S1 transistor, an S2 transistor, a primary winding, and a secondary winding. Both the S1 and S2 transistors are composed of an IGBT and an anti-parallel diode, and are connected in series in reverse in the circuit. The emitter of the S1 IGBT is connected to the emitter of the S2 IGBT. The collectors of the two IGBTs are connected to the two ends of the secondary winding. The gates of the S1 and S2 IGBTs are respectively connected to a PWM generator.

[0071] The adjustable reactor control method for the new energy grid-connected testing platform includes the following steps:

[0072] Step (1): Define a switching function f to control the IGBTs of transistors S1 and S2 to turn on and off, with the IGBTs of transistors S1 and S2 conducting complementaryly.

[0073]

[0074] Perform a Fourier expansion on f:

[0075]

[0076] In the formula, α is the duty cycle of the IGBT, k is the ratio of the secondary winding voltage period to the PWM wave period, F(α, k) is the Fourier expansion term; n is an integer in [1,∞], ω is the angular frequency, and t is time;

[0077] F(α,k)=sin(nωτ)+sin[nω(T c +τ)]-sinnωT c +sin[nω(2T c +τ)]

[0078] In the formula, τ is the conduction time in the PWM wave, ω is the voltage angular frequency, and Tc The period of the PWM wave;

[0079] Step (2): When the IGBT is turned on and off using PWM wave control, S1 and S2 are turned on alternately and complementaryly. The actual voltage value of the secondary winding is calculated through step (1). Ignoring higher harmonics and considering only the fundamental wave, we get:

[0080] u2=fU N sinωt=αU N sinωt

[0081] In the formula, u2 is the actual voltage of the secondary winding, U N Given the rated voltage of the secondary winding and the impedance value of the secondary winding, Z2, the current value of the secondary winding, i2, is obtained:

[0082]

[0083] Step (3): Based on the current of the secondary winding obtained in step (2), and assuming the turns ratio of the primary winding to the secondary winding is N, the voltage U of the primary winding is obtained. N1 The current value i1 of the primary winding;

[0084] Step (4): Obtain the voltage U of the primary winding according to step (3). N1 Given the current value i1 of the primary winding, the impedance Z1 of the primary winding is calculated.

[0085] Step (5): Based on the results obtained in step (4), pulses with different duty cycles are sent through the PWM generator. By changing the conduction and cutoff of transistors S1 and S2, the current of the secondary winding of the adjustable reactor is changed. The reverse magnetic flux generated changes the core reluctance of the adjustable reactor, thereby realizing continuous adjustment of the inductance value.

[0086] The inverter unit is a DC / AC inverter unit.

[0087] The transformer is an isolation step-up transformer.

[0088] The tested equipment includes wind turbines, photovoltaic systems, and energy storage devices.

[0089] In step (3), the voltage U of the primary winding N1 The formula for calculating the current value i1 of the primary winding is as follows:

[0090]

[0091] Therefore, the primary winding current is obtained as follows:

[0092]

[0093] In step (4), the impedance Z1 of the primary winding is calculated using the following formula:

[0094]

[0095] Example 3

[0096] like Figure 1 As shown, an adjustable reactor control method for a new energy grid-connected testing platform is disclosed. The new energy grid-connected testing platform includes a rectifier unit, a DC power supply, an inverter unit, an adjustable reactor, and a transformer; the inverter unit is a DC / AC inverter unit. The transformer is an isolation step-up transformer. The devices under test include wind turbines, photovoltaic systems, and energy storage devices.

[0097] The three-phase input voltage is connected to a DC power supply through a rectifier unit. The DC power supply is connected to the DC side of the DC / AC inverter unit. The AC side of the DC / AC inverter unit is filtered by an adjustable reactor and then connected to the device under test through an isolation step-up transformer. The device under test is a wind turbine, photovoltaic, or energy storage device.

[0098] like Figure 2 As shown, the sampling bidirectional IGBT is controlled by PWM to turn on and off, thereby controlling the secondary winding current. By changing the magnitude of the reverse magnetic flux generated by the secondary winding, the inductance of the adjustable reactor can be adjusted.

[0099] Step (1): Define a switching function f to control the IGBTs of transistors S1 and S2 to turn on and off, with the IGBTs of transistors S1 and S2 conducting complementaryly.

[0100]

[0101] Perform a Fourier expansion on f:

[0102]

[0103] In the formula, α is the duty cycle of the IGBT, k is the ratio of the secondary winding voltage period to the PWM wave period, F(α, k) is the Fourier expansion term; n is an integer in [1,∞], ω is the angular frequency, and t is time;

[0104] F(α,k)=sin(nωτ)+sin[nω(T c +τ)]-sinnωT c +sin[nω(2T c +τ)]

[0105] In the formula, τ is the conduction time in the PWM wave, ω is the voltage angular frequency, and T c The period of the PWM wave;

[0106] Step (2): When the IGBT is turned on and off using PWM wave control, S1 and S2 are turned on alternately and complementaryly. The actual voltage value of the secondary winding is calculated through step (1). Ignoring higher harmonics and considering only the fundamental wave, we get:

[0107] u2=fU N sinωt=αU N sinωt

[0108] In the formula, u2 is the actual voltage of the secondary winding, U N Given the rated voltage of the secondary winding and the impedance value of the secondary winding, Z2, the current value of the secondary winding, i2, is obtained:

[0109]

[0110] Step (3): Based on the current of the secondary winding obtained in step (2), and assuming the turns ratio of the primary winding to the secondary winding is N, the voltage U of the primary winding is obtained. N1 With current value i1:

[0111]

[0112] Therefore, the primary winding current is obtained as follows:

[0113]

[0114] Step (4): Based on the voltage and current values ​​of the primary winding obtained in step (3), the impedance Z1 of the primary winding is calculated using the following formula:

[0115]

[0116] Step (5): Based on the results obtained in step (4), pulses with different duty cycles are sent via PWM. By changing the on and off states of S1 and S2, the current in the secondary winding of the adjustable reactor is changed. The resulting reverse magnetic flux changes the reluctance of the reactor's core, thus achieving continuous adjustment of the inductance value. Changing the duty cycle α changes the impedance of the adjustable reactor. When α increases, the magnitude of the adjustable reactor's impedance decreases; when α decreases, the impedance of the adjustable reactor increases.

[0117] This invention provides an adjustable reactance control method for a new energy grid-connected monitoring platform. This method can linearly adjust the reactance, has a simple structure, and is easy to implement in engineering. It uses IGBT transistors, which are small, high-frequency switching devices with fast response speeds. Only a small LC filter is needed to remove high-order harmonics, reducing harmonic pollution. Figure 3 The simulation model of the adjustable reactor in the new energy grid-connected testing platform shown in Table 1 can obtain impedance data under different duty cycles.

[0118] Table 1 Simulation data under different duty cycles

[0119] PWM duty cycle α <![CDATA[Primary winding voltage U N1 > <![CDATA[Primary winding current i1]]> <![CDATA[Adjustable reactor impedance Z1]]> 0 193.0V 0.054A 3574.07Ω 0.2 190.7V 0.065A 2933.85Ω 0.5 170.2V 0.167A 1019.16Ω 0.8 146.1V 0.288A 507.29Ω 1 88.38V 0.577A 153.17Ω

[0120] As can be seen from Table 1, as the duty cycle of the PWM wave increases, the primary winding voltage of the adjustable reactor decreases, the primary winding current increases with the increase of the duty cycle, and the primary winding impedance of the adjustable reactor decreases with the increase of the duty cycle, thus realizing the linear adjustability of the adjustable reactor.

[0121] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An adjustable reactor control method for a new energy grid-connected detection platform, characterized in that, The new energy grid connection testing platform includes a rectifier unit, a DC power supply, an inverter unit, an adjustable reactor, and a transformer; The three-phase input voltage is connected to the DC power supply through the rectifier unit, the DC power supply is connected to the DC side of the inverter unit, and the AC side of the inverter unit is output through the adjustable reactor and then connected to the device under test through the transformer. The adjustable reactance includes transistor S1, transistor S2, a primary winding, and a secondary winding. Transistors S1 and S2 are each composed of an IGBT and an anti-parallel diode, and are connected in series in reverse in the circuit. The emitter of the IGBT of transistor S1 is connected to the emitter of the IGBT of transistor S2. The collectors of the two IGBTs are connected to the two ends of the secondary winding. The gates of the IGBTs of transistors S1 and S2 are respectively connected to a PWM generator. The adjustable reactor control method for the new energy grid-connected testing platform includes the following steps: Step (1): Define the switching function f to control the IGBTs of transistors S1 and S2 to turn on and off, with the IGBTs of transistors S1 and S2 conducting complementaryly. ； Perform a Fourier expansion on f: In the formula, α is the duty cycle of the IGBT, k is the ratio of the secondary winding voltage period to the PWM wave period, F(α, k) is the Fourier expansion term, and n is an integer in [1, ∞). ω is the angular frequency, and t is time; In the formula, The conduction time in the PWM wave. It is the voltage angular frequency. The period of the PWM wave; Step (2): When the IGBT is turned on and off using PWM wave control, S1 and S2 are turned on alternately and complementaryly. The actual voltage value of the secondary winding is calculated through step (1). Ignoring higher harmonics and considering only the fundamental wave, we get: In the formula, U is the actual voltage of the secondary winding. N Given the rated voltage of the secondary winding and the impedance value of the secondary winding, Z2, the current value of the secondary winding, i2, is obtained: ； Step (3): Based on the current of the secondary winding obtained in step (2), and assuming the turns ratio of the primary winding to the secondary winding is N, the voltage U of the primary winding is obtained. N1 The current value i1 of the primary winding; Step (4): Obtain the voltage U of the primary winding according to step (3). N1 The impedance Z1 of the primary winding is obtained by calculating the current value i1 of the primary winding. Step (5): Based on the results obtained in step (4), pulses with different duty cycles are sent through the PWM generator. By changing the conduction and cutoff of transistors S1 and S2, the current of the secondary winding of the adjustable reactor is changed. The reverse magnetic flux generated changes the core reluctance of the adjustable reactor, thereby realizing continuous adjustment of the inductance value.

2. The adjustable reactance control method for the new energy grid-connected detection platform according to claim 1, characterized in that, The inverter unit is a DC / AC inverter unit.

3. The adjustable reactance control method for the new energy grid-connected detection platform according to claim 1, characterized in that, The transformer is an isolation step-up transformer.

4. The adjustable reactance control method for the new energy grid-connected detection platform according to claim 1, characterized in that, The tested equipment includes wind turbines, photovoltaic systems, and energy storage devices.

5. The adjustable reactance control method for the new energy grid-connected detection platform according to claim 1, characterized in that, In step (3), the voltage U of the primary winding N1 The formula for calculating the current value i1 of the primary winding is as follows: Therefore, the primary winding current is obtained as follows: 。 6. The adjustable reactance control method for the new energy grid-connected detection platform according to claim 1, characterized in that, In step (4), the impedance Z1 of the primary winding is calculated using the following formula: 。

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