Three-phase imbalance few-sensor control method and system based on controlled impedance source

Abstract

The invention provides a three-phase imbalance few-sensor control method and system based on a controlled impedance source. The method is based on a controlled impedance source model and comprises two links of simulating steady-state resistance control and simulating time-varying impedance control. The analog steady-state resistance control is used for adjusting the average active power of the converter, and zero-static-error tracking of a power instruction is realized by adjusting equivalent resistance parameters; the simulation time-varying impedance control dynamically compensates the secondary active power pulsation of the direct current side caused by the imbalance of the power grid by introducing a double-frequency time-varying impedance component, so that the high-quality sinusoidal waveform of the grid-side current is maintained while the power oscillation is suppressed. Besides, the method only needs to collect the grid-side current of the converter without a power grid voltage sensor and a phase-locked loop, so that the hardware cost is reduced and the system reliability is improved. Meanwhile, the method has excellent robustness for asymmetry of input inductance parameters, and is simple in algorithm structure, low in operation load and suitable for engineering application.

Description

Technical Field

[0001] This invention relates to the field of power electronic control technology, and more specifically, to a sensorless control method for grid-side voltage control that balances sinusoidal grid-side current and constant DC-side active power under unbalanced grid-side operating conditions. Background Technology

[0002] With the rapid development of renewable energy generation and distributed energy storage systems, the three-phase voltage source converter (VSC), as a key interface connecting the power grid and DC loads / power sources, has crucial control performance. However, real-world power grids often experience voltage imbalances, which can lead to distortion of the VSC grid-side current and generate double-frequency active power pulsations on the DC side, severely impacting system stability and power quality.

[0003] Typically, to achieve high-performance control, VSC systems require AC voltage sensors to acquire grid voltage information for phase-locked loop synchronization or feedforward compensation. However, voltage sensors not only increase the hardware cost and size of the system, but their measurement noise or failures in harsh environments can also reduce system reliability. Therefore, control technology without grid voltage sensors has become a research hotspot.

[0004] Existing sensorless control methods mainly include observer-based strategies and virtual flux-based strategies. While these methods can estimate grid voltage, they typically rely on accurate system parameters and have high algorithmic complexity. In recent years, control strategies based on controlled impedance sources have attracted much attention due to their simplicity and lack of the need for phase-locked loops. However, traditional analog resistance control strategies are mostly only applicable to ideal balanced grids. When the grid voltage is unbalanced, suppressing power ripple often requires complex positive-to-negative sequence separation algorithms or the construction of special rotating coordinate systems, which sacrifices control simplicity and makes it difficult to simultaneously maintain the sinusoidal nature of the grid-side current and the constancy of the DC-side power.

[0005] Therefore, there is an urgent need to design a novel sensorless control method for unbalanced grid conditions, which can effectively suppress DC-side secondary power ripple while ensuring high-quality waveform of grid-side current without increasing hardware costs. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a sensorless control method that balances sinusoidal grid-side current with constant DC-side active power. The aim is to achieve safe and stable operation of the converter and high-quality grid connection under grid voltage imbalance conditions without the need for grid voltage sensors and phase-locked loops.

[0007] The technical solution of the present invention is as follows:

[0008] A sensorless control method for three-phase imbalance based on a controlled impedance source, the control method comprising the following steps:

[0009] Step 1: Calculate the required analog steady-state resistance r based on the power command P given by the converter. d / a;

[0010] Step 2: Based on the second harmonic active power ripple component P of the converter ripple Calculate the required simulated time-varying impedance x e ;

[0011] Step 3: Combine the DC and AC component port voltage control laws f(i,a) and h(i,x) respectively. e Obtain the converter port voltage output reference value u αβ * .

[0012] Step 1 specifically includes:

[0013] 'a' is calculated based on the relationship between the converter input and the steady-state resistance, where the relationship between the converter input and the analog resistance is:

[0014] ;

[0015] Among them, u α u β Let r be the port voltage component in a two-phase stationary coordinate system. d These are parameters that affect system stability.

[0016] Furthermore, the power component calculation method involved in step 2 is as follows: The converter grid-side current is collected and transformed to a two-phase stationary coordinate system; the instantaneous active power is obtained by combining it with the previous reference voltage; the AC component in the instantaneous active power is filtered out using a notch filter to obtain the DC active power component P. dc The second harmonic component of the instantaneous active power is extracted using a bandpass filter to obtain the second harmonic active power ripple component P. ripple .

[0017] Furthermore, in step 1, the given power command P* is compared with the DC active power component P. dc The difference is calculated and input into the proportional-integral controller to obtain the simulated steady-state resistance coefficient 'a', which is used to adjust the average active power of the converter. In step 2, the reference value is compared with the second harmonic active power ripple component P. ripple The difference is calculated and input into the resonant controller to obtain the simulated time-varying impedance x. e It is used to suppress active power oscillations on the DC side.

[0018] Furthermore, in step 3, a reference value u for the converter terminal voltage output is obtained. αβ * The specific calculation formula is as follows:

[0019] ;

[0020] The expression for the steady-state resistance control law f(i, a) is as follows:

[0021] ;

[0022] Time-varying impedance control law h(i,x) e The expression for ) is:

[0023] ;

[0024] Where g(⋅) is a function that makes the phase of the input signal lag by 90°, which can be implemented using SOGI in practice.

[0025] The present invention also provides a three-phase unbalanced sensorless control system based on a controlled impedance source, comprising: at least one processor; and at least one memory communicatively connected to the processor, wherein the memory stores program instructions executable by the processor, and the processor can execute the above-described control method by calling the program instructions.

[0026] The technical solution of the present invention has the following beneficial effects:

[0027] This invention only requires sampling the grid-side current of the converter, eliminating the need for grid voltage sensors and phase-locked loops, significantly reducing hardware costs and improving system reliability. By introducing simulated time-varying impedance, this invention can directly compensate for secondary active power ripple caused by grid imbalance in a two-phase stationary coordinate system, thereby ensuring the sinusoidal nature of the AC current while maintaining constant DC-side active power. Furthermore, this method eliminates the need for complex sequence extraction algorithms and rotating coordinate transformations, resulting in a simple control structure, low computational load, and ease of digital implementation. It also exhibits excellent robustness to input inductance parameter mismatch, making it suitable for practical engineering applications. Attached Figure Description

[0028] The features and advantages of the invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the drawings:

[0029] Figure 1 This is a structural block diagram of the converter according to an embodiment of the present invention;

[0030] Figure 2 This is a block diagram of the control algorithm of the control system in an embodiment of the present invention;

[0031] Figure 3 This is a flowchart of the control algorithm according to an embodiment of the present invention;

[0032] Figure 4 This is an equivalent schematic diagram of an embodiment of the present invention;

[0033] Figure 5 Experimental waveform diagram of an embodiment of the present invention. Detailed Implementation

[0034] The present invention will now be clearly and completely described in conjunction with the accompanying drawings and embodiments. The technical problems solved by the present invention and its beneficial effects will also be described. It should be noted that the described embodiments are only intended to facilitate the understanding of the present invention and do not limit it in any way.

[0035] Example 1:

[0036] This embodiment uses a three-phase converter system as an example for illustration. Figure 1 The diagram shows a three-phase converter, which includes an input AC voltage source, an input filter inductor, a switching transistor circuit, and a DC voltage source; the switching transistor circuit is composed of 6 IGBTs.

[0037] like Figure 2 , Figure 3 As shown in the figure, this embodiment provides a three-phase unbalanced sensorless control method based on a controlled impedance source. The specific control method is as follows:

[0038] Step 1: First, acquire the three-phase input current i on the grid side of the converter using a current sensor. abc The Clark transformation is used to convert it to a two-phase stationary coordinate system to obtain the current i. αβ .

[0039] Step 2: Next, the instantaneous active power of the converter is calculated based on the collected current. To achieve independent control of average power and power ripple, this invention introduces a filter stage:

[0040] Using a center frequency of ω g The notch filter removes the AC component from the instantaneous power and extracts the DC active power component P. dc ;

[0041] Using a center frequency of 2ω g The bandpass filter extracts the second harmonic component from the instantaneous power, obtaining the second harmonic active power ripple component P. ripple .

[0042] Step 3: The present invention includes two parallel control loops, which are used to adjust the average power and suppress the active power pulsation component, respectively.

[0043] 1. Average power control loop: The given power command P is... * With actual DC active power P dc The error is compared and input to the PI controller. The output of the PI controller is the analog steady-state resistance coefficient 'a'. This coefficient 'a' determines the magnitude of the steady-state resistance, thereby controlling the magnitude and direction of the average active power absorbed or generated by the converter.

[0044] 2. Active power ripple suppression control loop: This loop suppresses the second harmonic active power ripple component P. ripple The error is compared to 0 and input to the QPR controller. The controller's output is the analog time-varying impedance x. e The impedance x e It is a quantity that changes at a frequency of twice the normal frequency. Its function is to introduce a reverse power fluctuation component to offset the secondary power pulsation caused by grid imbalance.

[0045] Step 4: Voltage reference value synthesis based on the calculated coefficient 'a' and time-varying impedance 'x' e Each is combined with its corresponding control law. The reference voltage is composed of two superimposed parts: the first part is f(i,a), which physically represents the converter as a steady-state resistor. Its expression is:

[0046] ;

[0047] In the formula, r d α is a preset analog dynamic resistance used to ensure the small-signal stability of the system under all operating conditions (including rectification, inversion, and no-load); k is the damping coefficient, typically taken as 1.414. By adjusting α, the gain of this transfer function at the fundamental frequency can be changed, thereby adjusting the power.

[0048] The second part is the control law h(i,x) related to time-varying impedance. e The physical meaning of this is to insert a controlled time-varying impedance in series in the circuit. Its expression is:

[0049] ;

[0050] Where g(⋅) is a function that makes the phase of the input signal lag by 90°, which can be implemented using SOGI in practice;

[0051] Finally, by adding the two parts mentioned above, the reference value u of the converter terminal voltage output is obtained. αβ * :

[0052] ;

[0053] Figure 4The equivalent circuit principle of the above control strategy is illustrated. The converter is equivalent to a steady-state resistor and a time-varying resistor connected in series. Only the converter input current i needs to be collected. abc When the grid-side voltage is uneven, the active power on the DC side can remain constant, and the three-phase current on the grid side maintains a good sinusoidal property.

[0054] Figure 5 The experimental waveforms show the switching from conventional control to the control strategy proposed in this invention for a three-phase converter under grid voltage imbalance conditions.

[0055] During steady-state operation, the converter input current exhibits a sinusoidal waveform. Furthermore, upon switching to the method proposed in this invention, the active power on the DC side achieves smooth and constant operation. It can be observed that the second harmonic ripple of the active power is rapidly suppressed, and the converter input current remains undistorted. This demonstrates that the proposed simulated time-varying impedance control effectively addresses power fluctuations under grid imbalance, ensuring reliable and safe system operation.

[0056] Example 2:

[0057] This embodiment provides a three-phase unbalanced sensorless control system based on a controlled impedance source, comprising: at least one processor; and at least one memory communicatively connected to the processor, wherein the memory stores program instructions executable by the processor, and the processor can execute the control method in Embodiment 1 by calling the program instructions.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A sensorless control method for three-phase unbalance based on a controlled impedance source, characterized in that, The control method includes the following steps: Step 1: Calculate the required analog steady-state resistance r based on the power command P given by the converter. d / a; Step 2: Based on the second harmonic active power ripple component P of the converter ripple Calculate the required simulated time-varying impedance x e ; Step 3: Combine the steady-state resistance control law f(i,a) and the time-varying impedance control law h(i,x) e Obtain the converter port voltage output reference value u αβ * .

2. The three-phase unbalanced sensorless control method based on a controlled impedance source according to claim 1, characterized in that, Step 1 specifically includes: 'a' is calculated based on the relationship between the converter input and the steady-state resistance, where the relationship between the converter input and the analog resistance is: ； Among them, u α u β Let r be the port voltage component in a two-phase stationary coordinate system. d These are parameters that affect system stability.

3. The three-phase unbalanced sensorless control method based on a controlled impedance source according to claim 2, characterized in that, In step 2, the second-harmonic active power ripple component P ripple The calculation method is as follows: The converter grid-side current is collected and transformed to a two-phase stationary coordinate system to calculate the instantaneous active power. A notch filter is used to remove the AC component from the instantaneous active power to obtain the DC active power component P. dc The second harmonic component of the instantaneous active power is extracted using a bandpass filter to obtain the second harmonic active power ripple component P. ripple .

4. The three-phase unbalanced sensorless control method based on a controlled impedance source according to claim 3, characterized in that... In step 2, the simulated time-varying impedance x e The specific manifestations are as follows: ； Among them, X e γ represents the simulated time-varying impedance x e The time-varying impedance amplitude and phase angle information.

5. The three-phase unbalanced sensorless control method based on a controlled impedance source according to claim 4, characterized in that, In step 3, a reference value u for the converter port voltage output is obtained. αβ * The specific calculation formula is as follows: ； The steady-state resistance control law f(i,a) is expressed as follows: ； Time-varying impedance control law h(i, x) e The expression is: ； Where g(⋅) is a function that causes the input signal to lag by 90°.

6. A three-phase unbalanced sensorless control system based on a controlled impedance source, characterized in that, include: At least one processor; And at least one memory communicatively connected to the processor, wherein the memory stores program instructions executable by the processor, and the processor invokes the program instructions to perform the three-phase unbalanced sensorless control method as described in any one of claims 1 to 5.

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