A method for controlling an AC output circuit for testing the breaking capacity of a circuit breaker

Abstract

The present invention discloses an AC output circuit control method for testing the breaking capacity of a circuit breaker. The AC output circuit is composed of a supercapacitor, a single-phase inverter and a multi-magnetic circuit transformer. Considering the influence of factors such as transformer leakage inductance on current control, a double closed-loop control method combining the primary current model predictive control of the multi-magnetic circuit transformer and the secondary current PI effective value control is adopted. The system error is observed and compensated in the model predictive control by a state observer. In order to achieve a good control effect of the model predictive control, an online parameter identification method is used to establish a more accurate system model, and a dead time compensation method is used to reduce system harmonics. The control method has stable output current and small current harmonics, which provides an important means for realizing AC output of a single-phase inverter.

Description

Technical Field

[0001] The present invention relates to the technical field of single-phase inverter control, and in particular to an AC output circuit control method for testing the breaking capacity of a circuit breaker. Background Art

[0002] Common control methods for single-phase inverters include voltage-type control and current-type control. Voltage-type control indirectly controls the output current by controlling the output voltage. This control method is open-loop control. Its advantages include the lack of current feedback, a simple control structure, and relatively stable control effects. However, due to the lack of a current feedback link, energy loss is also relatively severe. Current-type control includes PI control, repetitive control, fuzzy control, sliding mode variable structure control, proportional resonance control, and model predictive control. PI control has a simple structure and stable control, but it cannot achieve zero-error control of AC quantities and cannot resolve the contradiction between rapidity and stability. Model predictive control has a fast response but requires a high degree of accuracy for the system model, and its control effect is affected by changes in system parameters. Summary of the Invention

[0003] The present invention proposes a dual-closed-loop single-phase inverter control method that combines primary-side model predictive control with secondary-side PI effective value control.

[0004] The present invention aims to provide an AC output circuit control method for testing the breaking capacity of a circuit breaker. The AC output circuit includes a supercapacitor, three single-phase inverter units, a multi-magnetic circuit transformer, a short-circuit protection device, and a circuit breaker test piece. The AC output circuit control method includes the following steps:

[0005] Establish a continuous model of the single-phase inverter system, obtain the optimal voltage vector, and obtain the switching signal that controls the IGBT operation through SVPWM modulation;

[0006] By considering the influence of system loss factors on system control, a realistic model of the single-phase inverter system is established, and the linear time-varying observer designed in combination with the extended state observer is used to obtain the system error.

[0007] Online parameter identification is used to modify the impedance of the control model in real time to achieve better control effects.

[0008] Furthermore, the continuous model of the single-phase inverter system is:

[0009]

[0010] Among them, R represents the resistance of the AC output circuit, L represents the inductance of the AC output circuit, i t Indicates the inverter output current, u t Indicates the inverter output voltage;

[0011] The real model of the single-phase inverter system is:

[0012]

[0013] Where d represents the systematic error.

[0014] Furthermore, the discrete model of the system obtained by central difference is:

[0015]

[0016] Among them, i t (k+1) is the inverter output current at the next moment, i t (k) is the inverter output current at the current moment, i t (k-1) is the inverter output current at the previous moment, T S is the inverter control period.

[0017] Using deadbeat control command i t (ref)=i t (k+1), where i t (ref) is the given inverter output current, then the optimal voltage vector is:

[0018]

[0019] Among them, u′ t is the optimal voltage vector.

[0020] Furthermore, let u t =u and d=x2, the real model of the single-phase inverter system can be expressed as follows:

[0021]

[0022] Among them, a=R, b=1.

[0023] Furthermore, the real model of the single-phase inverter system is combined with the observer as follows:

[0024]

[0025] Where z2 represents the observed error, β1 represents the first calculation constant, β1 = 2ω-R; e1 = z1-x1 represents the error between the current observation value and the actual value, β2 represents the second calculation constant, β2 = ω 2 ;ω represents the bandwidth of the selected extended state observer;

[0026] According to the convergence of the extended state observer, the observed error z2 is the system error d.

[0027] Furthermore, the online parameter identification obtains the system impedance and the transformation ratio of the multi-magnetic circuit transformer based on the sampled inverter output voltage, inverter output current, and secondary current of the multi-magnetic circuit transformer.

[0028] Furthermore, the inverter output voltage and the inverter output current are generally assumed to be:

[0029]

[0030] Among them, u t Indicates the inverter output voltage, i t represents the inverter output current, U represents the voltage amplitude of the AC component, I represents the current amplitude of the AC component, ω is the angular frequency, represents the initial phase angle of the voltage, Indicates the initial phase angle of the current.

[0031] Furthermore, the inverter output voltage and the inverter output current are multiplied by sinωt and cosωt respectively to obtain the q-axis component u of the voltage. tq , the d-axis component of the voltage u td , the q-axis component of the current i tq and the d-axis component of the current i td :

[0032]

[0033] Among them, u tq 、u td 、i tq and i td Each contains a DC component and and a double frequency AC component, the u tq 、u td 、i tq and i td The corresponding DC component can be obtained by inputting the low-pass filter.

[0034] Furthermore, the impedance of the system is obtained according to the DC component, and the impedance of the system is:

[0035]

[0036] The impedance of the system model is dynamically adjusted according to the impedance of the system, so that the control effect is more accurate.

[0037] Furthermore, the AC output circuit control method further includes the following steps:

[0038] The error voltage is calculated based on the single-phase inverter unit IGBT conduction voltage drop, diode tube voltage drop, IGBT turn-on delay and turn-off delay, dead time, DC bus voltage and control period, and then the error voltage is compensated to the inverter output voltage:

[0039]

[0040] Among them, u ce Indicates the on-state voltage drop of IGBT, u df Indicates the diode voltage drop, t on , t off and t dead They represent the turn-on delay, turn-off delay and dead time of IGBT respectively, u dc Indicates the DC bus voltage, T S represents the inverter control period, and Δu represents the error voltage.

[0041] The beneficial effects of the present invention include:

[0042] The present invention adopts a dual closed-loop control strategy that combines primary-side model predictive control with secondary-side PI effective value control, while taking advantage of the rapidity of model predictive control and the stability of PI control, so that the system has the advantages of stable output waveform, small output harmonics, fast dynamic response, and strong anti-interference ability.

[0043] The present invention adopts a state observer to observe system errors, and actively considers the influence of errors caused by system losses on system control.

[0044] The present invention adopts an online parameter identification method to detect the change of system impedance in real time, establishes a more accurate system model, and makes the control of the system more stable.

[0045] The present invention adopts dead time compensation to make the error between the actual output voltage and the given output voltage smaller, reduce the harmonics of the system, and make the control of the system more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a circuit topology diagram of an AC output circuit for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of the effective value of the secondary current output when parameters are matched in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0048] Figure 3This is a schematic diagram of the effective value of the secondary current output when parameters do not match in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of the effective value of the secondary current output when parameters do not match with compensation in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0050] Figure 5 This is a waveform diagram of a secondary current of 5000A output for 30s in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0051] Figure 6 This is a waveform diagram of a secondary current of 5000A output for 30s in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0052] Figure 7 This is a schematic diagram of a waveform of a secondary current of 10,000 A output for 3 seconds in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0053] Figure 8 This is a schematic diagram of a waveform of a secondary current of 10,000 A output for 3 seconds in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0054] Figure 9 This is a schematic diagram of a waveform of a secondary current of 20,000 A output for 1 second in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0055] Figure 10 This is a schematic diagram of a waveform of a secondary current of 20,000 A output for 1 second in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention;

[0056] Figure 11 This is a schematic diagram of a 0.2s waveform of a secondary current of 5000A in an AC output circuit control method for testing the breaking capacity of a circuit breaker provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0057] The technical solutions of the present invention are described in more detail below with reference to the accompanying drawings. The present invention includes but is not limited to the following embodiments.

[0058] As attached Figure 1The present invention provides an AC output circuit control method for circuit breaker breaking capacity testing. This method controls the AC output circuit for circuit breaker breaking capacity testing to output 3kA-50kA AC current to test the circuit breaker's breaking capacity. The AC output circuit includes a supercapacitor, three single-phase inverter units, a multi-magnetic transformer, a short-circuit protection device, and a circuit breaker test piece.

[0059] The positive and negative poles of the supercapacitor are respectively connected to three single-phase inverter units; each single-phase inverter unit contains two IGBT half-bridge modules, the collector of the upper tube of each IGBT half-bridge module is connected to the positive pole of the supercapacitor, and the emitter of the lower tube is connected to the negative pole of the supercapacitor; the outputs of the three single-phase inverter units are respectively connected to the three primary windings of the multi-magnetic circuit transformer, and the secondary winding of the multi-magnetic circuit transformer is connected to the circuit breaker test piece; the overvoltage short-circuit protection device is connected in parallel with the circuit breaker test piece.

[0060] The present invention takes into account factors such as transformer leakage inductance and adopts a dual closed-loop control method that combines primary-side model predictive control with secondary-side PI effective value control. The specific control method includes:

[0061] In the primary side model prediction, taking one of the inverters as an example, a continuous model of the single-phase inverter system is first established:

[0062]

[0063] Among them, R represents the resistance of the AC output circuit, L represents the inductance of the AC output circuit, i t Indicates the inverter output current, u t Indicates the inverter output voltage.

[0064] Assuming that factors such as system loss have an impact on system control, the true model of the single-phase inverter system can be expressed as:

[0065]

[0066] Where d represents the systematic error.

[0067] The discrete model of the system obtained by using the central difference of the true model of the system can be expressed as:

[0068]

[0069] Among them, i t (k+1) is the inverter output current at the next moment, i t (k) is the inverter output current at the current moment, i t (k-1) is the inverter output current at the previous moment, T Sis the inverter control period.

[0070] Using deadbeat control command i t (ref)=i t (k+1), where i t (ref) is the given inverter output current, then the optimal voltage vector is:

[0071]

[0072] Among them, u′ t It is the optimal voltage vector, and after SVPWM modulation, the switching signal that controls the IGBT action can be obtained.

[0073] Assumption u t =u and d = x2, then the real model of the single-phase inverter system can be expressed as follows:

[0074]

[0075] Where a = R, b = 1. The linear time-varying observer designed based on the above formula combined with the extended state observer can be rewritten as:

[0076]

[0077] Wherein, z2 represents the observation error, β1 represents the first calculation constant, e1=z1-x1 represents the error between the current observation value and the actual value, and β2 represents the second calculation constant.

[0078] Due to the convergence of the extended state observer, the error equation can be obtained as follows:

[0079]

[0080] Among them, e2 is equivalent to the error between the observed value and the actual value of the system error.

[0081] right Taking the derivative we get:

[0082]

[0083] When the disturbance of the system is constant, let β1=2ω-R, β2=ω 2 , where ω is the bandwidth of the selected extended state observer. If the roots of the system equations are all in the left half plane, the system is stable and e1 converges to 0. Similarly, it can be proved that e2 converges. Therefore, the extended state observer is convergent, and it can be obtained that z2 is approximately equal to x2. The observed value of z2 is the system error d.

[0084] As attached Figure 2-4As shown in the figure, the current output simulation waveform when model predictive control is used, Figure 2 is the effective value of the output AC current when the given system impedance matches the actual impedance parameters. It can be seen that when the given current is 20000A, the current output error is less than 1%; Figure 3 The output AC current is the effective value when the given resistance is 0.5 times greater than the actual resistance and the given inductance is 0.2 times smaller than the actual inductance. It can be seen that the current output error is approximately 5% when the given current is 20000A. Figure 4 The given resistance is 0.5 times larger than the actual resistance, the given inductance is 0.2 times smaller than the actual inductance, and the state observer is added to observe and compensate the system error and output the effective value of the AC current. It can be seen that when the current output is given at 20000A, it can be well controlled at the given value. Figure 2-Figure 4 The simulation results shown can achieve a good control effect when using model predictive control with compensation. It can be seen that when using model predictive control, a relatively accurate modeling of the system model is required.

[0085] Because model predictive control requires an accurate system model to achieve effective control when controlling the primary current, online parameter identification is used to modify the impedance of the control model in real time to achieve superior control results. Online parameter identification is used to determine the system impedance and the transformation ratio of the multi-magnetic transformer based on the sampled inverter output voltage, inverter output current, and multi-magnetic transformer secondary current. This is done by making general assumptions about the inverter output voltage and inverter output current, as shown in the following equation:

[0086]

[0087] Among them, u t Indicates the inverter output voltage, i t represents the inverter output current, U represents the voltage amplitude of the AC component, I represents the current amplitude of the AC component, ω is the angular frequency, represents the initial phase angle of the voltage, Indicates the initial phase angle of the current.

[0088] will u t and i t Multiply by sinωt and cosωt respectively to get u tq 、u td 、i tq and i td , as shown below:

[0089]

[0090] As shown in the above formula, the q-axis component u of the voltage tq , the d-axis component of the voltage u td , the q-axis component of the current itq and the d-axis component of the current i td Each contains a DC component and And a double frequency AC component, u tq 、u td 、i tq and i td Input the low-pass filter to get the corresponding DC component. and It contains the phase and amplitude information of voltage and current, so the impedance of the system can be calculated based on the DC component. The calculation method is as follows:

[0091]

[0092] The above formula can be used to dynamically adjust the impedance of the system model, making the control effect more precise. At the same time, the transformer ratio can be obtained based on the ratio between the primary output current and the secondary output current.

[0093] Dead time compensation for the on-state voltage drop u based on the single-phase inverter unit IGBT ce , diode voltage drop u df , IGBT turn-on delay t on and turn-off delay t off , dead time t dead , DC bus voltage u dc and control period T S The error voltage Δu is obtained. The specific mathematical model is:

[0094]

[0095] Then the error voltage is compensated to the inverter output voltage u t middle.

[0096] As attached Figure 5-11 As shown in the figure, the experimental results of the secondary current output at different gears are obtained by measuring the Rogowski coil. The vertical axis 1V corresponds to the actual output 20000A. Figure 5 and Figure 6 The secondary current RMS value is set to 5000A and a 30s waveform is output; Figure 7 and Figure 8 The secondary current RMS value is set to 10000A and a 3s waveform is output; Figure 9 and Figure 10 The secondary current RMS value is set to 20000A and the 1s waveform is output; Figure 11The 0.2s waveform is output when the effective value of the secondary current is set to 50000 A. It can be seen that the output current waveform of the control strategy of the present invention is a relatively good sine waveform, the current can reach the set value relatively quickly, the dynamic response speed is fast, and the control is stable and reliable.

[0097] The present invention is not limited to the above-mentioned specific embodiments. A person skilled in the art can implement the present invention in a variety of other specific embodiments based on the embodiments and the contents disclosed in the drawings. Therefore, any design that adopts the design structure and ideas of the present invention and makes some simple transformations or changes falls within the scope of protection of the present invention.

Claims

1. An AC output circuit control method for testing the breaking capacity of a circuit breaker, wherein the AC output circuit comprises a supercapacitor, three single-phase inverter units, a multi-magnetic circuit transformer, a short-circuit protection device and a circuit breaker test piece, characterized in that: The AC output circuit control method comprises the following steps: Establish a continuous model of the single-phase inverter system, obtain the optimal voltage vector, and obtain the switching signal for controlling the IGBT action through SVPWM modulation; Through the influence of system loss factors on system control, a real model of the single-phase inverter system is established, and the linear time-varying observer designed in combination with the extended state observer is used to obtain the system error; The impedance of the control model is modified in real time using online parameter identification; The continuous model of the single-phase inverter system is: Where, R represents the resistance of the AC output circuit, L represents the inductance of the AC output circuit, i t Indicates the inverter output current, u t Indicates the inverter output voltage; The real model of the single-phase inverter system is: Where d represents the system error; u t =u and d=x2, the real model of the single-phase inverter system can be expressed as follows: Wherein, a=R, b=1; The real model of the single-phase inverter system combined with the observer is: Wherein, z2 represents the observed error, β1 represents the first calculation constant, β1=2ω-R; e1=z1-x1 represents the error between the current observation value and the actual value, β2 represents the second calculation constant, β2=ω 2 ; ω represents the bandwidth of the selected extended state observer; According to the convergence of the extended state observer, the observed error z2 is the system error d.

2. The AC output circuit control method according to claim 1, characterized in that: The discrete model of the system obtained by using the central difference for the real model of the system is: Among them, i t (k+1) is the inverter output current at the next moment, i t (k) is the inverter output current at the current moment, i t (k-1) is the inverter output current at the previous moment, T S is the inverter control period; Use deadbeat control command i t (ref) = i t (k+1), where i t (ref) is the given inverter output current, then the optimal voltage vector is: Among them, u′ t is the optimal voltage vector.

3. The AC output circuit control method according to claim 1, characterized in that: The online parameter identification obtains the system impedance and the transformation ratio of the multi-magnetic circuit transformer based on the sampled inverter output voltage, inverter output current, and secondary current of the multi-magnetic circuit transformer.

4. The AC output circuit control method according to claim 3, characterized in that: The inverter output voltage and inverter output current make general assumptions: Among them, u t Indicates the inverter output voltage, i t represents the inverter output current, U represents the voltage amplitude of the AC component, I represents the current amplitude of the AC component, ω represents the angular frequency, represents the initial phase angle of the voltage, Represents the initial phase angle of the current.

5. The AC output circuit control method according to claim 4, characterized in that: The inverter output voltage and the inverter output current are multiplied by sinωt and cosωt respectively to obtain the q-axis component u of the voltage. tq , the d-axis component of the voltage u td , the q-axis component of the current i tq and the d-axis component of the current i td : Among them, u tq 、u td 、i tq and i td Each contains a DC component and and a double frequency AC component, which converts the u tq 、u td 、i tq and i td The corresponding DC component can be obtained by inputting a low-pass filter.

6. The AC output circuit control method according to claim 5, characterized in that: The impedance of the system is obtained according to the DC component, and the impedance of the system is: The impedance of the system model is dynamically adjusted based on the impedance of the system.

7. The AC output circuit control method according to claim 1, characterized in that: The AC output circuit control method further comprises the following steps: The error voltage is calculated based on the on-state voltage drop of the single-phase inverter unit IGBT, the tube voltage drop of the diode, the on-delay and off-delay of the IGBT, the dead time, the DC bus voltage and the control cycle, and then the error voltage is compensated to the inverter output voltage: Among them, u ce Indicates the on-state voltage drop of IGBT, u df Represents the diode voltage drop, t on ,t off and t dead They represent the turn-on delay, turn-off delay and dead time of IGBT respectively, u dc Indicates the DC bus voltage, T S represents the inverter control period, and Δu represents the error voltage.

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