Control method and device for measuring and calculating stability of double-end flexible interconnection system

Abstract

The invention relates to a control method and device for measuring and calculating the stability of a double-end flexible interconnection system, and the method comprises the steps: enabling a load converter to be equivalent to a constant-power load based on a large-signal averaging model of a three-phase PWM rectifier with a load, and estimating the stability boundary of the three-phase PWM rectifier with the constant-power load; applying a disturbance signal within the stable boundary, sampling the output side voltage and current of the three-phase PWM rectifier, and making a difference between the output side voltage and an output reference voltage, and taking the difference as a voltage drop on an output equivalent resistor of a Buck Boost system port; the voltage drop is sent to an impedance simulation link, and a Buck Boost system port output current reference instruction value is obtained; the difference value between the current reference instruction value and the output side current is sent to a current loop controller for closed-loop control, and the duty ratio change of the Buck Boost system is obtained; and the duty ratio change of the Buck Boost system is compared with the sawtooth wave of the modulation module, and a switching signal of the power device is generated according to the comparison result. According to the invention, a better stability measuring and calculating mode can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution, and particularly to a control method and device for measuring the stability of a double-ended flexible interconnection system. Background Art

[0002] With the adjustment of the energy structure and the development of the power system towards higher flexibility and renewable energy integration, the double-ended flexible interconnection system has gradually become an important research topic in the field of power engineering. The key lies in overcoming the deficiencies of traditional power interconnection systems in aspects such as dynamic response, load regulation, and stability guarantee through flexible control technology. This technology is particularly suitable for cross-regional power grid dispatching, optimizing power supply and demand matching, and enhancing the regulation ability of the power grid in the face of the volatility of large-scale renewable energy. However, the double-ended flexible interconnection system has high complexity, high investment and operation costs, complex scheduling and coordination, and the access of large-scale renewable energy may lead to an increase in the volatility of power flow, thus affecting the stability of the system.

[0003] In addition, how to establish an accurate power grid model, coordinate control among multiple dispatching points, conduct steady-state and transient stability analysis in a complex and changing environment, and make reasonable control decisions is an important part of stability assessment. Although flexible control devices have high adjustment capabilities, in the face of sudden large-scale disturbances, the response time of the double-ended flexible interconnection system may be slow. Currently, most of its stability tests are based on actual lines, with complex processes and difficulty in simulating the real usage environment, having the drawbacks of low efficiency and high cost. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a control method and device for measuring the stability of a double-ended flexible interconnection system, which can achieve a better stability measurement method.

[0005] The technical solution adopted by the present invention to solve its technical problems is: to provide a control method for measuring the stability of a double-ended flexible interconnection system, including the following steps:

[0006] Based on the large-signal average model of a three-phase PWM rectifier with a load, the load converter is equivalent to a constant power load, and the stability boundary of the three-phase PWM rectifier with a constant power load is estimated;

[0007] Apply a disturbance signal within the stability boundary, sample the output-side voltage and current of the three-phase PWM rectifier, subtract the output-side voltage from the output reference voltage, and use the obtained difference as the voltage drop across the equivalent resistance at the output of the Buck_Boost system port;

[0008] The voltage drop across the equivalent resistance of the Buck_Boost system port output is fed into the impedance simulation link to obtain the reference instruction value of the Buck_Boost system port output current;

[0009] The difference between the current reference instruction value and the output side current is fed into the current loop controller for closed-loop control to obtain the duty cycle change of the Buck_Boost system;

[0010] The duty cycle change of the Buck_Boost system is compared with the sawtooth wave of the modulation module, and the switching signal of the power device is generated according to the comparison result.

[0011] When estimating the stability boundary of the three-phase PWM rectifier with a constant power load, it is estimated based on the sufficient condition for the stability of the three-phase PWM rectifier with a converter load under large-signal disturbances under PI control. The sufficient condition is: where P CPL_PI is the maximum power point at which the rectifier remains stable after the sudden increase in the power of the load converter during PI control, C is the bus capacitor, R s is the equivalent series resistance on the grid side, K ip is the proportional coefficient of the current loop controller, L is the grid side filter inductor, v dcmin is the minimum value of the DC bus voltage, K vp is the proportional coefficient of the voltage loop controller, e d and i d are the components of the three-phase grid voltage and current in the d-q coordinate system respectively, v d is the d-axis control target voltage, K vi is the integral coefficient of the voltage loop controller, v dcref is the bus voltage given value.

[0012] The reference instruction value of the Buck_Boost system port output current is obtained through calculation, where i dref is the reference instruction value of the Buck_Boost system port output current, U dref is the output reference voltage, U dcB is the output side voltage, L V is the line virtual inductor, R V is the line virtual resistance, and s is the complex frequency domain variable in the Laplace transform.

[0013] The duty cycle change of the Buck_Boost system is obtained through calculation, where ΔD is the duty cycle change of the Buck_Boost system, K ip is the proportional coefficient of the current loop controller, K ii is the integral coefficient of the current loop controller, idref is the reference instruction value of the output current of the Buck_Boost system port, i dc is the output side current, and s is the complex frequency domain variable in the Laplace transform.

[0014] The control method for measuring the stability of the double-ended flexible interconnected system further includes:

[0015] Using the small-signal modeling method, derive the expression of the open-loop output impedance of the three-phase PWM rectifier, and measure the open-loop output impedance;

[0016] According to the closed-loop reduced-order small-signal control method of the three-phase PWM rectifier, obtain the expression of the closed-loop output impedance of the three-phase PWM rectifier, and measure the closed-loop output impedance.

[0017] The expression of the open-loop output impedance of the three-phase PWM rectifier is: where Z out_o (s) is the open-loop output impedance of the three-phase PWM rectifier, L is the grid-side filter inductor, R s is the grid-side equivalent series resistance, C is the bus capacitor, D dl is the control duty cycle, and s is the complex frequency domain variable in the Laplace transform.

[0018] The expression of the closed-loop output impedance of the three-phase PWM rectifier is: where Z out (s) is the closed-loop output impedance of the three-phase PWM rectifier, L is the grid-side filter inductor, R s is the grid-side equivalent series resistance, V dc is the bus voltage, G ci (s) is the transfer function of the current loop controller, expressed as: K ip and K ii are respectively the proportional coefficient and integral coefficient of the current loop controller, G cv (s) is the transfer function of the voltage loop controller, expressed as: K vp and K vi are respectively the proportional coefficient and integral coefficient of the voltage loop controller, D dl is the control duty cycle, and M1(s), M2(s) and M3(s) are all intermediate variables, and the expressions are respectively: and C is the bus capacitor, I d is the d-axis current, and s is the complex frequency domain variable in the Laplace transform.

[0019] The technical solution adopted by the present invention to solve its technical problems is: to provide a control device for measuring the stability of a double-ended flexible interconnected system, including:

[0020] A stable boundary estimation module, which is used to equivalent the load converter to a constant power load based on the large-signal average model of a three-phase PWM rectifier with a load, and estimate the stable boundary of the three-phase PWM rectifier with a constant power load;

[0021] An application sampling module, which is used to apply a disturbance signal within the stable boundary, sample the output-side voltage and current of the three-phase PWM rectifier, subtract the output-side voltage from the output reference voltage, and use the obtained difference as the voltage drop across the equivalent resistance at the output port of the Buck_Boost system;

[0022] An impedance simulation module, which is used to send the voltage drop across the equivalent resistance at the output port of the Buck_Boost system into an impedance simulation link to obtain the reference command value of the output current at the output port of the Buck_Boost system;

[0023] A closed-loop control module, which is used to send the difference between the current reference command value and the output-side current into a current-loop controller for closed-loop control to obtain the duty cycle change of the Buck_Boost system;

[0024] A generation module, which is used to compare the duty cycle change of the Buck_Boost system with the sawtooth wave of the modulation module, and generate the switching signal of the power device according to the comparison result.

[0025] The stable boundary estimation module estimates based on the sufficient condition for the stability of a three-phase PWM rectifier with PI control under large-signal disturbance when it is loaded with a converter. The sufficient condition is: Where P CPL_PI is the maximum power point at which the rectifier remains stable after the power of the load converter suddenly increases during PI control, C is the bus capacitor, R s is the equivalent series resistance on the grid side, K ip is the proportional coefficient of the current-loop controller, L is the grid-side filter inductor, v dcmin is the minimum value of the DC bus voltage, K vp is the proportional coefficient of the voltage-loop controller, e d and i d are the components of the three-phase grid voltage and current in the d-q coordinate system respectively, v d is the d-axis control target voltage, K vi is the integral coefficient of the voltage-loop controller, v dcref is the bus voltage given value.

[0026] The impedance simulation module calculates the reference command value of the output current at the output port of the Buck_Boost system through where i drefis the reference instruction value of the output current of the Buck_Boost system port, U dref is the output reference voltage, U dcB is the output side voltage, L V is the line virtual inductor, R V is the line virtual resistor, and s is the complex frequency domain variable in the Laplace transform.

[0027] The closed-loop control module calculates the duty cycle change of the Buck_Boost system, where ΔD is the duty cycle change of the Buck_Boost system, and K ip is the proportional coefficient of the current loop controller, K ii is the integral coefficient of the current loop controller, i dref is the reference instruction value of the output current of the Buck_Boost system port, i dc is the output side current, and s is the complex frequency domain variable in the Laplace transform.

[0028] The control device for measuring the stability of the dual-terminal flexible interconnected system further includes:

[0029] An open-loop output impedance measurement module, which is used to derive the expression of the open-loop output impedance of the three-phase PWM rectifier by using the small-signal modeling method and measure the open-loop output impedance;

[0030] A closed-loop output impedance measurement module, which is used to obtain the expression of the closed-loop output impedance of the three-phase PWM rectifier according to the closed-loop reduced-order small-signal control method of the three-phase PWM rectifier and measure the closed-loop output impedance.

[0031] The expression of the open-loop output impedance of the three-phase PWM rectifier derived by the open-loop output impedance measurement module is: where Z out_o (s) is the open-loop output impedance of the three-phase PWM rectifier, L is the grid-side filter inductor, R s is the grid-side equivalent series resistance, C is the bus capacitor, D dl is the control duty cycle, and s is the complex frequency domain variable in the Laplace transform.

[0032] The expression of the closed-loop output impedance of the three-phase PWM rectifier obtained by the closed-loop output impedance measurement module is: where Z out (s) is the closed-loop output impedance of the three-phase PWM rectifier, L is the grid-side filter inductor, R s is the grid-side equivalent series resistance, V dc is the bus voltage, G ci (s) is the transfer function of the current loop controller, expressed as: K ipand K ii are the proportional coefficient and integral coefficient of the current loop controller, respectively, and G cv (s) is the transfer function of the voltage loop controller, expressed as: K vp and K vi are the proportional coefficient and integral coefficient of the voltage loop controller, respectively, and D dl is the control duty cycle, and M1(s), M2(s) and M3(s) are all intermediate variables, and the expressions are respectively: and C is the bus capacitor, I d is the d-axis current, and s is the complex frequency domain variable in the Laplace transform.

[0033] The technical solution adopted by the present invention to solve its technical problems is: to provide an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, and when the processor executes the computer program, the steps of the above control method for measuring the stability of the double-ended flexible interconnected system are realized.

[0034] The technical solution adopted by the present invention to solve its technical problems is: to provide a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the above control method for measuring the stability of the double-ended flexible interconnected system are realized.

[0035] Beneficial effects

[0036] Due to the adoption of the above technical solution, compared with the prior art, the present invention has the following advantages and positive effects: The present invention reproduces various states of the DC line through the simulation technology of the impedance of the flexible DC transmission line, measures its own stability by measuring the load resistance on the DC side, and then uses the virtual impedance to measure the stability of the interconnection interaction, realizing a better stability measurement method. Description of the drawings

[0037] Figure 1 is a flowchart of the control method for measuring the stability of the double-ended flexible interconnected system in the first embodiment of the present invention;

[0038] Figure 2 is a diagram for measuring the stability of the double-ended flexible interconnection with virtual impedance and DC / DC;

[0039] Figure 3 is an equivalent circuit diagram of the average model of the three-phase PWM rectifier;

[0040] Figure 4 is a closed-loop reduced-order small-signal control block diagram of the three-phase PWM rectifier;

[0041] Figure 5It is a schematic diagram of a three-phase PWM rectifier topology when the load is equivalent to a constant power load;

[0042] Figure 6 It is a circuit operation process diagram of a single-phase four-switch BUCK-BOOST converter;

[0043] Figure 7 It is the main working waveform diagram of the synchronous control of the pair of tubes. Specific embodiments

[0044] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0045] The first embodiment of the present invention relates to a control method for measuring the stability of a dual-terminal flexible interconnected system, and this method can be applied to, for example, Figure 2 the measuring circuit of the dual-terminal interconnection stability shown as follows. In this measuring circuit, the converters VSC-A and VSC-B at both ends of the flexible DC system are connected through a four-switch Buck_Boost system. By controlling the port characteristics of the four-switch Buck_Boost system, the impedance change situation of the actual line is simulated, so as to realize the stability of the flexible DC interconnected system under different power grid conditions. As can be seen from Figure 2 it, the Buck_Boost system can be equivalent to an impedance model connected in series on the line. Therefore, by adding a line impedance simulation strategy in the control, the line impedance simulation value can be adjusted online to realize the simulation characteristic of equivalently changing the real line impedance.

[0046] As shown in Figure 1 the following, the control method for measuring the stability of the dual-terminal flexible interconnected system in this embodiment includes the following steps:

[0047] Step 1, using the small-signal modeling method, derive the expression of the open-loop output impedance of the three-phase PWM rectifier and measure the open-loop output impedance.

[0048] In this step, define d d and d q as the equivalent duty cycles in the d-q coordinate system. By averaging the switching period of the mathematical model of the three-phase PWM rectifier in the d-q coordinate system, the following can be obtained:

[0049]

[0050] where, R s is the equivalent series resistance on the grid side, L is the filter inductance on the grid side, C is the bus capacitor, ω0 is the fundamental angular frequency, and t is time. is the average value of the bus voltage over a switching period, is the average value of the load current over a switching period, and are respectively the average values of the grid voltage in the d-q coordinate system over a switching period, and are respectively the average values of the grid-side current in the d-q coordinate system over a switching period.

[0051] The corresponding average model equivalent circuit is as shown in Figure 3 . It should be noted that writing the load term in different forms will have a great impact on the stability judgment result. When the load term is written as v dc (t) / R L , the peak value of the output impedance of the three-phase PWM rectifier is significantly smaller, resulting in a situation that is actually unstable being misjudged as stable.

[0052] Let the duty cycle satisfy:

[0053]

[0054] where d d1 and d q1 respectively represent the control duty cycles output by the current loop in the d-q coordinates, and are respectively the average values of the d-q voltages output by the current loop control over a switching period.

[0055] The switched-capacitor average model of the decoupled three-phase PWM rectifier is obtained as:

[0056]

[0057] Apply perturbations to and d d1 :

[0058]

[0059] Then the small-signal response is:

[0060]

[0061] The equilibrium point of the three-phase PWM rectifier can be obtained:

[0062]

[0063] where I d is the d-axis current, I L is the load current, E d is the effective value of the three-phase grid voltage component in the d-q coordinate system, V dc is the bus voltage, D dlTo control the duty cycle.

[0064] The open-loop output impedance Z(s) of the three-phase PWM rectifier is obtained as: out_o (s):

[0065]

[0066] where s is the complex frequency domain variable in the Laplace transform.

[0067] Step 2: According to the closed-loop reduced-order small-signal control method of the three-phase PWM rectifier, the expression of the closed-loop output impedance of the three-phase PWM rectifier is obtained, and the closed-loop output impedance is measured.

[0068] Figure 4 is the closed-loop reduced-order small-signal control block diagram of the three-phase PWM rectifier. G(s) is the transfer function of the current-loop PI controller, and G(s) is the transfer function of the voltage-loop PI controller. Their expressions are respectively: ci (s) is the transfer function of the current-loop PI controller, and G(s) is the transfer function of the voltage-loop PI controller. cv (s) According to the closed-loop reduced-order small-signal control method of the three-phase PWM rectifier, the transfer functions of the PI controllers of the current loop and the voltage loop are respectively:

[0069]

[0070] where K and K are respectively the proportional coefficient and the integral coefficient of the current-loop controller, and K and K are respectively the proportional coefficient and the integral coefficient of the voltage-loop controller. ip and K ii are respectively the proportional coefficient and the integral coefficient of the current-loop controller, and K vp and K vi are respectively the proportional coefficient and the integral coefficient of the voltage-loop controller.

[0071] According to Figure 4 , the closed-loop transfer function matrix equation of the three-phase PWM rectifier can be obtained, and the closed-loop output impedance Z(s) of the three-phase PWM rectifier is obtained as: out (s):

[0072]

[0073] In the formula, the intermediate variables M1(s), M2(s), and M3(s) are respectively:

[0074]

[0075]

[0076] Substitute the relevant parameters into the formula, and the Bode plot of the output impedance of the three-phase PWM rectifier can be obtained. By observing whether it intersects with the input impedance of the load converter, its stability can be judged according to the Middlebrook stability criterion.

[0077] Step 3: Based on the large-signal average model of the three-phase PWM rectifier with a load, the load converter is equivalent to a constant power load, and the stability boundary of the three-phase PWM rectifier with a constant power load is estimated.

[0078] When conducting research related to large-signal stability, the load converter is equivalent to a constant power load. The topology of the three-phase PWM rectifier after load equivalence is as Figure 5 shown. According to the input power and output power balance relationship, we can obtain:

[0079]

[0080] where, i dc and v dc are the output current and voltage on the DC side of the bridge arm respectively, v d and v q are the control target voltages on the d-q axes respectively, and i d and i q are the components of the three-phase grid current in the d-q coordinate system respectively.

[0081] The voltage potential function B(v) is derived as a first-order matrix:

[0082]

[0083] where, P CPL is the power of the constant power load.

[0084] Next, the second-order partial derivative B vv_PI (v) of the voltage potential function B(v) with respect to voltage is derived. Considering the quadrature-axis current of the three-phase PWM rectifier operating in the unity power factor state, we can obtain:

[0085]

[0086] where, K ip is the proportional coefficient of the current loop controller, K ip is the proportional coefficient of the voltage loop controller, K vi is the integral coefficient of the voltage loop controller, e d is the component of the three-phase grid voltage in the d-q coordinate system, and v dcref is the given value of the bus voltage.

[0087] Define the maximum power point P CPL_PI at which the rectifier remains stable after the power of the load converter suddenly increases during PI control. The sufficient condition for the stability of the three-phase PWM rectifier with PI control under large-signal disturbances when driving a converter load is:

[0088]

[0089] where, vdcmin is the minimum value of the DC bus voltage.

[0090] Using this formula, the maximum sudden increase range of the load power that the three-phase PWM rectifier with a constant power load can withstand can be estimated, that is, the stability boundary.

[0091] Step 4: Apply a disturbance signal within the stability boundary, sample the output-side voltage and current of the three-phase PWM rectifier, subtract the output-side voltage from the output reference voltage, and use the obtained difference as the voltage drop across the equivalent resistance at the output port of the Buck_Boost system.

[0092] In this step, when applying the disturbance signal within the stability boundary, the DC / DC system can adopt a synchronous control method. The switching pulses of switch S1 and switch S4 are the same, the switching pulses of switch S2 and switch S3 are the same, and the switching pulses of switch S1 and switch S2 are complementary.

[0093] Step 5: Send the voltage drop across the equivalent resistance at the output port of the Buck_Boost system into the impedance simulation link to obtain the reference command value of the output current at the output port of the Buck_Boost system.

[0094] According to the impedance simulation control strategy, for the four-switch Buck_Boost converter system, under the operation of line impedance simulation, the relationship between the output voltage and the output current is:

[0095]

[0096] where, i dref is the reference command value of the output current at the output port of the Buck_Boost system, U dref is the output reference voltage, U dcB is the output-side voltage, L V is the line virtual inductor, R V is the line virtual resistance.

[0097] Step 6: Send the difference between the current reference command value and the output-side current into the current loop controller for closed-loop control to obtain the duty cycle change of the Buck_Boost system.

[0098] In this step, the expression for the duty cycle change output by the current loop of the Buck_Boost converter is as follows:

[0099]

[0100] where, ΔD is the duty cycle change of the Buck_Boost system, K ip is the proportional coefficient of the current loop controller, K ii is the integral coefficient of the current loop controller, idref is the reference instruction value of the output current of the Buck_Boost system port, i dc is the output-side current.

[0101] The current inner loop control bandwidth is relatively high. Usually, the cut-off frequency of the current inner loop is about one-tenth of the switching frequency. Therefore, the influence of the dynamic response of the current inner loop can be ignored, that is, the output current of the Buck_Boost converter is the current instruction value. At this time, according to the relationship between its output voltage and current, the equivalent impedance on the line can be obtained as the set value of the line virtual impedance link. When the line impedance parameters to be simulated are determined, it can be directly set as the line virtual inductor L V and the line virtual resistor R V , thus realizing the simulation of the line impedance.

[0102] Step 7, compare the duty cycle change of the Buck_Boost system with the sawtooth wave of the modulation module, and generate the switching signal of the power device according to the comparison result.

[0103] When the switch tubes S1 and S4 are conducting and the switch tubes S2 and S3 are off, the equivalent circuit is as shown in Figure 6 (a) in, and the current I L flows through the inductor coil L to store energy. When the switch tubes S1 and S4 are off and the equivalent circuit is as shown in Figure 6 (b) in, when the switch tubes S2 and S3 are conducting, the current I L decreases, the inductor coil generates a self-induced electromotive force in the opposite direction, and the output voltage is U out , the capacitor charges and stores energy, and buffers the change of U out .

[0104] When the switch tubes S1 and S4 of the four-switch Buck_Boost converter perform switching actions synchronously under the same control signal, the sizes of its two independent duty cycles are always the same, that is, it can be considered that there is only one duty cycle. At this time, the four-switch Buck_Boost converter can be equivalent to a traditional single-switch Buck-Boost converter in terms of circuit characteristics, and the only difference is that the polarities of its input and output voltages are the same.

[0105] Figure 7 The main working waveforms of the four-switch Buck_Boost converter under this control method are given. It can be seen that during the time when the switch tubes S1 and S4 are conducting or off simultaneously, the change amount of the inductor current is the inductor current pulsation amount, and the corresponding inductor voltages are U in and U out . Thus, the mathematical derivation of the inductor current pulsation amount in the synchronous control mode of the pair of tubes can be carried out.

[0106] As shown inFigure 7 As shown, when switch S1 and switch S4 are turned on and switch S2 and switch S3 are turned off, the voltage drop across the inductor is U during this period. in And the inductor current increases linearly. This period is set as T. ON , duty cycle D1 = D = (T ON / T OFF ) < 1, T s is the switching frequency, and we can get:

[0107]

[0108] When switch S1 and switch S4 are turned off and switch S2 and switch S3 are turned on, the current in inductor L decreases, and the voltage across the inductor is negative on the left and positive on the right. Since the current in the inductor cannot change suddenly, the current in inductor L conducts through capacitor C and the load for freewheeling. This period is set as T OFF , duty cycle D2 = 1 - D = (T ON / T OFF ) < 1, and we can get:

[0109]

[0110] Similarly, according to the volt-second balance principle, we can get ΔI L (+) = ΔI L (-), then we can solve the relationship between the input voltage U in , output voltage U out :

[0111]

[0112] By adjusting the duty cycle D, step-up and step-down control can be performed. When D > 1 / 2, the system operates in the boost mode. When 0 < D < 1 / 2, the system operates in the buck mode. Since the inductor only transfers current to the load when switch S1 and switch S4 are turned off and switch S2 and switch S3 are turned on, the average value of the inductor current over the entire switching cycle is not equal to the output current. The output current is only equal to the average value of the current at this time, so the following formula is given:

[0113]

[0114] In the formula, I L(avg) is the average value of the inductor current, I O is the output current, T s is the control period. It can be seen from the above formula that the average value of the inductor current is proportional to the output current, and this ratio can be adjusted by changing the duty cycle D.

[0115] It is not difficult to find that in this embodiment, various states of the DC line can be reproduced through the simulation technology of the impedance of the flexible DC transmission line. The stability of the DC side with a load resistor is measured, and then the virtual impedance is used to measure the stability of the interconnection and interaction, realizing a better stability measurement method.

[0116] The second embodiment of the present invention relates to a control device for measuring the stability of a two-terminal flexible interconnection system, including:

[0117] A stability boundary estimation module, configured to, based on the large-signal average model of the three-phase PWM rectifier with a load, equivalent the load converter to a constant power load, and estimate the stability boundary of the three-phase PWM rectifier with a constant power load;

[0118] An applied sampling module, configured to apply a disturbance signal within the stability boundary, sample the output-side voltage and current of the three-phase PWM rectifier, subtract the output-side voltage from the output reference voltage, and use the obtained difference as the voltage drop across the equivalent resistance at the output port of the Buck_Boost system;

[0119] An impedance simulation module, configured to send the voltage drop across the equivalent resistance at the output port of the Buck_Boost system into an impedance simulation link to obtain the current reference command value at the output port of the Buck_Boost system;

[0120] A closed-loop control module, configured to send the difference between the current reference command value and the output-side current into a current-loop controller for closed-loop control to obtain the duty cycle change of the Buck_Boost system;

[0121] A generation module, configured to compare the duty cycle change of the Buck_Boost system with the sawtooth wave of the modulation module, and generate the switching signal of the power device according to the comparison result.

[0122] The stability boundary estimation module is estimated based on the sufficient condition for the stability of the three-phase PWM rectifier with a PI control and a converter load under large-signal disturbances. The sufficient condition is: Where P CPL_PI is the maximum power point at which the rectifier remains stable after the power of the load converter suddenly increases during PI control, C is the bus capacitor, R s is the equivalent series resistance on the grid side, K ip is the proportional coefficient of the current-loop controller, L is the grid-side filter inductor, v dcmin is the minimum value of the DC bus voltage, K vp is the proportional coefficient of the voltage-loop controller, e d and i d are the components of the three-phase grid voltage and current in the d-q coordinate system respectively, v d is the d-axis control target voltage, K viis the integral coefficient of the voltage loop controller, v dcref is the given value of the bus voltage.

[0123] The impedance simulation module calculates the reference instruction value of the output current at the Buck_Boost system port through where i dref is the reference instruction value of the output current at the Buck_Boost system port, U dref is the reference output voltage, U dcB is the output side voltage, L V is the virtual inductance of the line, R V is the virtual resistance of the line, and s is the complex frequency domain variable in the Laplace transform.

[0124] The closed-loop control module calculates the duty cycle change of the Buck_Boost system through where ΔD is the duty cycle change of the Buck_Boost system, K ip is the proportional coefficient of the current loop controller, K ii is the integral coefficient of the current loop controller, i dref is the reference instruction value of the output current at the Buck_Boost system port, i dc is the output side current.

[0125] The control device for measuring the stability of the dual-terminal flexible interconnected system further includes:

[0126] An open-loop output impedance measurement module, which is used to derive the expression of the open-loop output impedance of the three-phase PWM rectifier by using the small-signal modeling method and measure the open-loop output impedance;

[0127] A closed-loop output impedance measurement module, which is used to obtain the expression of the closed-loop output impedance of the three-phase PWM rectifier according to the closed-loop reduced-order small-signal control method of the three-phase PWM rectifier and measure the closed-loop output impedance.

[0128] The expression of the open-loop output impedance of the three-phase PWM rectifier derived by the open-loop output impedance measurement module is: where Z out_o (s) is the open-loop output impedance of the three-phase PWM rectifier, L is the grid-side filter inductor, R s is the grid-side equivalent series resistance, C is the bus capacitor, D dl is the control duty cycle, and s is the complex frequency domain variable in the Laplace transform.

[0129] The expression of the closed-loop output impedance of the three-phase PWM rectifier obtained by the closed-loop output impedance measurement module is: where Z out(s) is the closed-loop output impedance of the three-phase PWM rectifier, L is the grid-side filtering inductor, and R s is the grid-side equivalent series resistance, and V dc is the bus voltage, and G ci (s) is the transfer function of the current-loop controller, expressed as: K ip and K ii are the proportional coefficient and integral coefficient of the current-loop controller respectively, and G cv (s) is the transfer function of the voltage-loop controller, expressed as: K vp and K vi are the proportional coefficient and integral coefficient of the voltage-loop controller respectively, D dl is the control duty ratio, and M1(s), M2(s) and M3(s) are all intermediate variables, and the expressions are respectively: and C is the bus capacitor, I d is the d-axis current, and s is the complex frequency domain variable in the Laplace transform.

[0130] The third embodiment of the present invention relates to an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the control method for measuring the stability of the dual-terminal flexible interconnection system in the first embodiment.

[0131] The fourth embodiment of the present invention relates to a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the steps of the control method for measuring the stability of the dual-terminal flexible interconnection system in the first embodiment.

[0132] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories and optical memories, etc.) containing computer-usable program codes.

[0133] This application is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing device to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing device generate a means for implementing the functions specified in one or more of the flows Figure 1 one or more of the flows and / or blocks Figure 1 or one or more of the blocks.

[0134] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, such that the instructions stored in the computer-readable memory generate a manufacture including the instruction method, and the instruction method implements the functions specified in one or more of the flows Figure 1 one or more of the flows and / or blocks Figure 1 or one or more of the blocks.

[0135] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more of the flows Figure 1 one or more of the flows and / or blocks Figure 1 or one or more of the blocks.

[0136] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A control method for measuring the stability of a double-ended flexible interconnected system, characterized in that It includes the following steps: Based on the large-signal average model of the three-phase PWM rectifier with a load, the load converter is equivalent to a constant power load, and the stability boundary of the three-phase PWM rectifier with a constant power load is estimated; Apply a perturbation signal within the stability boundary, sample the output-side voltage and current of the three-phase PWM rectifier, subtract the output reference voltage from the output-side voltage, and use the obtained difference as the voltage drop across the equivalent resistance at the output port of the Buck_Boost system; Feed the voltage drop across the equivalent resistance at the output port of the Buck_Boost system into the impedance simulation link to obtain the reference command value of the output current at the output port of the Buck_Boost system; Feed the difference between the reference command value of the current and the output-side current into the current-loop controller for closed-loop control to obtain the duty-cycle change of the Buck_Boost system; Compare the duty-cycle change of the Buck_Boost system with the sawtooth wave of the modulation module, and generate the switching signal of the power device according to the comparison result.

2. The control method for measuring the stability of a double-ended flexible interconnected system according to claim 1, characterized in that When estimating the stability boundary of the three-phase PWM rectifier with a constant power load, it is estimated based on the sufficient condition for the stability of the three-phase PWM rectifier with a PI control under large-signal perturbations when driving a converter load. The sufficient condition is: Among them, P CPL_PI is the maximum power point at which the rectifier remains stable after the sudden increase in the power of the load converter during PI control. C is the bus capacitor, and R s is the equivalent series resistance on the grid side, K ip is the proportional coefficient of the current loop controller, L is the grid side filter inductor, and v dcmin is the minimum value of the DC bus voltage, K vp is the proportional coefficient of the voltage loop controller, e d and i d are the components of the three-phase grid voltage and current in the d-q coordinate system respectively, v d is the d-axis control target voltage, K vi is the integral coefficient of the voltage loop controller, and v dcref is the bus voltage set value.

3. The control method for measuring the stability of a double-ended flexible interconnected system according to claim 1, characterized in that, The reference instruction value of the output current of the Buck_Boost system port is obtained through calculation, where i dref is the reference instruction value of the output current of the Buck_Boost system port, U dref is the output reference voltage, U dcB is the output-side voltage, L V is the line virtual inductance, R V is the line virtual resistance, and s is the complex frequency domain variable in the Laplace transform.

4. The control method for measuring the stability of a double-ended flexible interconnected system according to claim 1, characterized in that The duty cycle variation of the Buck_Boost system is obtained through calculation, where ΔD is the duty cycle variation of the Buck_Boost system, and K ip is the proportional coefficient of the current loop controller, and K ii is the integral coefficient of the current loop controller, i dref is the reference command value of the output current of the Buck_Boost system port, i dc is the output side current, and s is the complex frequency domain variable in the Laplace transform.

5. The control method for measuring the stability of a double-ended flexible interconnected system according to claim 1, characterized in that, It also includes: Using the small-signal modeling method, derive the expression of the open-loop output impedance of the three-phase PWM rectifier and measure the open-loop output impedance; According to the closed-loop reduced-order small-signal control method of the three-phase PWM rectifier, obtain the expression of the closed-loop output impedance of the three-phase PWM rectifier and measure the closed-loop output impedance.

6. The control method for measuring the stability of a double-ended flexible interconnected system according to claim 5, characterized in that, The expression of the open-loop output impedance of the three-phase PWM rectifier is as follows: Among them, Z out_o (s) is the open-loop output impedance of the three-phase PWM rectifier, L is the grid-side filtering inductor, and R s is the grid-side equivalent series resistance, C is the bus capacitor, D dl is the control duty cycle, and s is the complex frequency domain variable in the Laplace transform.

7. The control method for measuring the stability of a dual-terminal flexible interconnected system according to claim 5, characterized in that, The expression of the closed-loop output impedance of the three-phase PWM rectifier is: Among them, Z out (s) is the closed-loop output impedance of the three-phase PWM rectifier, L is the grid-side filtering inductor, and R s is the grid-side equivalent series resistance, V dc is the bus voltage, G ci (s) is the transfer function of the current-loop controller, expressed as: K ip and K ii are respectively the proportional coefficient and integral coefficient of the current-loop controller, G cv (s) is the transfer function of the voltage-loop controller, expressed as: K vp and K vi are the proportional coefficient and integral coefficient of the voltage loop controller respectively, D dl is the control duty cycle, M1(s), M2(s) and M3(s) are all intermediate variables, and the expressions are respectively: and where C is the bus capacitance, I d is the d-axis current, and s is the complex frequency domain variable in the Laplace transform.

8. A control device for measuring and calculating the stability of a double-ended flexible interconnected system, characterized in that, It includes: A stability boundary estimation module, which is used to, based on the large-signal average model of the three-phase PWM rectifier with a load, equivalent the load converter to a constant power load, and estimate the stability boundary of the three-phase PWM rectifier with a constant power load; an application and sampling module, which is used to apply a perturbation signal within the stability boundary, sample the output-side voltage and current of the three-phase PWM rectifier, subtract the output reference voltage from the output-side voltage, and use the obtained difference as the voltage drop across the equivalent resistance at the output port of the Buck_Boost system; An impedance simulation module, which is used to feed the voltage drop across the equivalent resistance at the output port of the Buck_Boost system into the impedance simulation link to obtain the reference command value of the output current at the output port of the Buck_Boost system; A closed-loop control module, which is used to feed the difference between the reference command value of the current and the output-side current into the current-loop controller for closed-loop control to obtain the duty-cycle change of the Buck_Boost system; A generation module, which is used to compare the duty-cycle change of the Buck_Boost system with the sawtooth wave of the modulation module, and generate the switching signal of the power device according to the comparison result.

9. The control device for measuring the stability of the double-ended flexible interconnected system according to claim 8, characterized in that, The stability boundary estimation module is estimated based on the sufficient condition for the stability of the three-phase PWM rectifier with a PI control under large-signal perturbations when driving a converter load. The sufficient condition is: Among them, P CPL_PI is the maximum power point at which the rectifier remains stable after the sudden increase in the power of the load converter during PI control. C is the bus capacitor, and R s is the equivalent series resistance on the grid side, K ip is the proportional coefficient of the current loop controller, L is the grid-side filter inductor, and v dcmin is the minimum value of the DC bus voltage, K vp is the proportional coefficient of the voltage loop controller, e d and i d are the components of the three-phase grid voltage and current in the d-q coordinate system respectively, v d is the d-axis control target voltage, K vi is the integral coefficient of the voltage loop controller, and v dcref is the bus voltage set value.

10. The control device for measuring the stability of a double-ended flexible interconnected system according to claim 8, characterized in that, The impedance simulation module calculates the reference instruction value of the output current of the Buck_Boost system port through where i dref is the reference instruction value of the output current of the Buck_Boost system port, U dref is the output reference voltage, U dcB is the output side voltage, L V is the line virtual inductor, R V is the line virtual resistor, and s is the complex frequency domain variable in the Laplace transform.

11. The control device for measuring the stability of a double-ended flexible interconnected system according to claim 8, characterized in that, The closed-loop control module calculates the duty cycle change of the Buck_Boost system through where ΔD is the duty cycle change of the Buck_Boost system, K ip is the proportional coefficient of the current loop controller, K ii is the integral coefficient of the current loop controller, i dref is the reference command value of the output current of the Buck_Boost system port, i dc is the output-side current, and s is the complex frequency domain variable in the Laplace transform.

12. The control device for measuring the stability of a dual-terminal flexible interconnected system according to claim 8, characterized in that, It also includes: The open-loop output impedance measurement module is used to derive the expression of the open-loop output impedance of the three-phase PWM rectifier by using the small-signal modeling method and measure the open-loop output impedance; The closed-loop output impedance measurement module is used to obtain the expression of the closed-loop output impedance of the three-phase PWM rectifier according to the closed-loop reduced-order small-signal control method of the three-phase PWM rectifier and measure the closed-loop output impedance.

13. The control device for measuring the stability of a double-ended flexible interconnected system according to claim 12, wherein The expression of the open-loop output impedance of the three-phase PWM rectifier derived by the open-loop output impedance measurement module is: Among them, Z out_o (s) is the open-loop output impedance of the three-phase PWM rectifier, L is the grid-side filter inductor, R s is the grid-side equivalent series resistance, C is the bus capacitor, D dl is the control duty cycle, and s is the complex frequency domain variable in the Laplace transform.

14. The control device for measuring the stability of a dual-terminal flexible interconnected system according to claim 12, characterized in that, The expression of the closed-loop output impedance of the three-phase PWM rectifier obtained by the closed-loop output impedance measurement module is: Among them, Z out (s) is the closed-loop output impedance of the three-phase PWM rectifier, L is the grid-side filter inductor, R s is the grid-side equivalent series resistance, V dc is the bus voltage, G ci (s) is the transfer function of the current-loop controller, expressed as: K ip and K ii are respectively the proportional coefficient and integral coefficient of the current-loop controller, G cv (s) is the transfer function of the voltage-loop controller, expressed as: K vp and K vi are the proportional coefficient and integral coefficient of the voltage loop controller respectively, D dl is the control duty cycle, M1(s), M2(s) and M3(s) are all intermediate variables, and the expressions are respectively: and C is the bus capacitance, I d is the d-axis current, and s is the complex frequency domain variable in the Laplace transform.

15. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the control method for measuring the stability of the two-terminal flexible interconnected system as described in any one of claims 1-7.

16. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the control method for measuring the stability of the two-terminal flexible interconnected system as described in any one of claims 1-7.

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