Control method and system for wideband impedance measurement device suitable for direct current distribution system

Abstract

The application discloses a control method and system of a wideband impedance measuring device suitable for a direct current power distribution system, and the wideband impedance measuring device mainly comprises a signal disturbance injection unit, a voltage and current signal acquisition unit and a wideband impedance calculation unit. The signal disturbance injection unit is composed of a DC / DC / AC power submodule and a filter circuit. The DC / DC / AC power submodule is composed of a DAB converter, a direct current side capacitor and a SiC single-phase full bridge. The front-stage DAB converter of the signal disturbance injection device adopts outer loop voltage proportional integral single-phase shift control, the rear-stage H bridge considers open loop control of direct current side voltage fluctuation when voltage is injected, and the on and off of the single-phase full bridge power device are controlled through bipolar SPWM modulation; current inner loop proportional integral control is adopted when current is injected. The application makes the system have higher reliability and faster dynamic response, and meets the requirements of wideband disturbance output impedance measurement in the scene of large-scale optical storage new energy power generation equipment direct current system.

Description

Technical Field

[0001] The present invention relates to the technical field of impedance measurement device development in renewable energy power generation, and in particular to a control method and system for a broadband impedance measurement device suitable for a DC power distribution system. Background Art

[0002] With the increasing number of DC loads such as large data centers, electric vehicle charging stations, and communications equipment, as well as the high proportion and large-capacity decentralized integration of DC distributed power sources such as photovoltaics, the safe and stable operation of DC distribution systems has attracted widespread attention. Solar photovoltaic power generation is one of the fastest-growing and most promising renewable energy power generation industries. With the large-scale integration of photovoltaic power generation, the increasing number of photovoltaic power generation equipment, and the rapid growth of loads such as electrical equipment, the energy system is characterized by high renewable energy penetration, high proportion of power electronic equipment, and high load growth rate ("three highs"), facing challenges in terms of system operation mode and reliability. Furthermore, when operating independently, the DC distribution network system integrating large-scale renewable energy is a weak inertia system dominated by power electronic equipment. The system is highly time-varying and has diverse operating modes. The lack of inertia in the DC distribution network, the random fluctuations of photovoltaic power generation, and the unpredictable load all pose significant challenges to the stable control of system voltage and frequency. Furthermore, power electronic loads, such as charging stations, require power conversion through corresponding converters. These converters exhibit constant power characteristics under closed-loop control, resulting in negative damping in the system, which also poses challenges to the safe and stable operation of the DC distribution network.

[0003] The impedance method based on frequency domain theory is one of the most commonly used methods for analyzing oscillation problems in grid-connected systems of renewable energy converters. Its basic idea is to regard the converter and AC power grid as two independent subsystems, use the impedance matrix to describe the external characteristics of the subsystems, and use the impedance ratio of the subsystems to judge the stability of the system. Since the system parameters and control parameters of existing renewable energy devices are difficult to obtain, it is difficult to carry out refined impedance modeling of renewable energy power generation equipment. Therefore, in order to solve the stability control problems caused by the large-scale access of renewable energy to the DC distribution network, the development of an impedance measurement device suitable for the DC distribution system has important practical significance for the stability research of the DC distribution network system. At present, most of the impedance measurement devices developed at home and abroad are for AC systems, and there is little research on DC distribution systems. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a control method and system for a wide-band impedance measurement device suitable for a DC power distribution system in response to the shortcomings of the existing technology, so as to meet the demand for accurate measurement of wide-band output impedance in scenarios where large-scale photovoltaic and energy storage are connected to DC systems.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a control method for a broadband impedance measurement device applicable to a DC power distribution system, comprising the following steps:

[0006] S1, at the starting point of each sampling period, the DC side voltages Udc1 and Udc2 of the primary and secondary sides of the DAB converter and the DC side voltage vdc2 of the subsequent H-bridge converter in the sub-power module unit of the broadband impedance measurement device are measured. dc Take samples;

[0007] S2, the voltage command signal U ref1 、U ref2 The voltage U on both sides of the primary and secondary sides of the DAB converter obtained by sampling dc1 、U dc2 The voltage error ΔU1 and ΔU2 are obtained by subtracting them; the voltage error ΔU1 and ΔU2 are controlled by the voltage outer loop PI and the values ​​obtained by the limit link and the gain index k pwm Multiply them to get the modulated signal u r1 、u r2 ; The modulated signal u r1 、u r2 Perform single phase shift modulation to obtain the duty cycle signal of the primary and secondary side switches in the DAB converter, and control the on and off of the DAB converter switches.

[0008] When voltage disturbance is injected, the DC side voltage command value V dc Divide by the actual DC side voltage v of the single-phase H-bridge DC / AC converter dc , get the amplitude M of the modulated waveform a ; According to the frequency instruction ω, initial phase instruction and M a , the H-bridge modulation wave is obtained as t is the time, After bipolar SPWM multi-level modulation, the control signal of the subsequent H-bridge switch tube is obtained to control the on and off of the subsequent H-bridge power device;

[0009] When the current disturbance is injected, the command signal Iref is subtracted from the sampled output current If of the wide-band disturbance injection device to obtain the current deviation value ΔI; the current deviation value ΔI is controlled by the current inner loop PI and then the value is limited by the gain index k. pwm Multiply them to get the modulated signal u r3 , the modulated signal u r3 Through PWM modulation, the switch control signal is obtained when the current disturbance is injected, thereby controlling the on and off of the subsequent H-bridge power device.

[0010] In actual renewable energy grid-connected systems, since the impedance of the power grid is often smaller than the impedance of renewable energy equipment, when series voltage disturbance injection is used, the disturbance voltage output on the grid side is small and easily affected by noise, making it impossible to accurately measure the grid impedance; when parallel current disturbance injection is used, it is impossible to accurately measure the impedance of renewable energy power generation equipment. Using the method of the present invention, when it is necessary to accurately measure the grid impedance, the grid impedance can be measured by a parallel current injection system using current closed-loop control; when it is necessary to accurately measure renewable energy power generation equipment, a series voltage injection system can be used to measure renewable energy power generation equipment. Different disturbance injection control methods can also be selected according to different grid impedance strengths to obtain accurate impedance characteristics of the DC distribution system.

[0011] The transfer function of the voltage outer loop PI control is: where K p is the proportional coefficient of PI control, K i is the integral coefficient of PI control.

[0012] K p The value is 0.0002, K i The value is 0.1.

[0013] The transfer function of the current inner loop PI control is: where K p1 is the proportional coefficient of PI control, K i1 is the integral coefficient of PI control.

[0014] K p1 The value is 20, K i1 The value is 0.5.

[0015] As an inventive concept, the present invention also provides a control system for a wide-band impedance measurement device suitable for a DC power distribution system, comprising a memory, a processor, and a computer program stored in the memory; the processor executes the computer program to implement the steps of the above method.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention meets the refinement requirements of the simulation model of power generation equipment in the new energy power generation base of the DC distribution network system, and fills the gap in the accurate measurement method and equipment of the wide-band impedance characteristics in the DC distribution network system scenario. The device adopts a DC / DC / AC structure and can directly draw power from the DC bus without the need for an additional DC source, which reduces both the cost and the size of the equipment. The method of disturbance injection can also be freely selected according to the different systems to improve the measurement accuracy. The present invention can change the control method according to the strength of different DC distribution network systems, and can accurately obtain the impedance characteristics of new energy. In addition, the control of disturbance injection is different, and the grid impedance of the DC distribution system can also be accurately measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a system structure diagram of a wide-band impedance measurement device applicable to a DC power distribution system according to an embodiment of the present invention;

[0018] Figure 2 This is a control diagram of a control method for a wideband impedance measurement device applicable to a DC power distribution system according to an embodiment of the present invention;

[0019] Figure 3 The system voltage and current waveforms after a disturbance voltage is added to a 375V DC power distribution system according to an embodiment of the present invention;

[0020] Figure 4 The system voltage and current waveforms after a disturbance current is added to a 375V DC power distribution system according to an embodiment of the present invention;

[0021] Figure 5 The output impedance characteristics of the Buck converter and its simulation measurement results according to an embodiment of the present invention are shown. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0023] Example 1

[0024] Figure 1 The following is a diagram showing the system structure of a broadband impedance measurement device for a DC power distribution system according to an embodiment of the present invention. The broadband impedance measurement device system for a DC power distribution system includes a current and voltage signal acquisition unit, a broadband voltage disturbance injection unit, and a broadband impedance calculation unit. The disturbance injection source can selectively inject a small disturbance voltage or current into the system, which responds with a small disturbance current and voltage, and collects the voltage and current to calculate the impedance. The specific calculation formula is as follows:

[0025]

[0026] The broadband voltage disturbance injection unit in the broadband impedance measurement device for DC power distribution systems consists of a DC / DC / AC power unit and a filtering circuit. The DC / DC / AC power submodule comprises a DAB converter, DC-side capacitors, and a SiC single-phase full-bridge. The output is directly connected to the DC bus system under test through the filtering circuit. To ensure practical application, the device is equipped with a power distribution cabinet and a switching cabinet, which can directly draw power from the 375V DC bus and facilitate device startup and shutdown.

[0027] Figure 2 This is a block diagram of a control method for a wideband impedance measurement device for a DC power distribution system according to an embodiment of the present invention, which mainly includes the following steps:

[0028] 1) At the starting point of each sampling period, the DC side voltage U of the primary and secondary sides of the DAB converter in the sub-power module unit of the broadband impedance measurement device is measured. dc1 、U dc2 and the DC side voltage v of the subsequent H-bridge converter dc Sampling is performed and the data converted by the AD converter is sent to the DSP controller.

[0029] 2) The voltage command signal U ref1 、U ref2 The voltage U on both sides of the primary and secondary sides of the DAB converter obtained by sampling dc1 、U dc2 Difference is made to obtain voltage errors ΔU1 and ΔU2.

[0030] 3) The voltage error ΔU1 and ΔU2 are obtained by the voltage outer loop PI control and then the values ​​are limited and combined with the gain index k pwm Multiplication can get the modulated signal u r1 、u r2 .

[0031] 4) Modulate the signal u r1 、u r2 Then single phase shift modulation is performed to obtain the duty cycle signals T1, T2, T3, T4, T5, T6, T7, and T8 of the primary and secondary side switches in the DAB converter to control the on and off of the DAB converter switches.

[0032] 5) When the voltage disturbance is selected, the switch signal S is enabled. r =1, the DC side voltage command value V dc Divide by the actual DC side voltage v of the single-phase H-bridge DC / AC converter dc , get the amplitude M of the modulated waveform aBy dividing the direct voltage instruction by the actual value as a modulation factor, the active power output of the H-bridge can be adjusted during the fluctuation of the direct voltage, thereby improving the dynamic performance of the voltage disturbance injection device.

[0033] 6) According to the frequency instruction ω, the initial phase instruction and M a , the H-bridge modulation wave is obtained as t is time, and After bipolar SPWM multi-level modulation, the H-bridge switch control signals S1, S2, S3 and S4 of the latter stage are obtained, so as to control the conduction and turn-off of the power devices of the latter stage H-bridge.

[0034] 7) When the current disturbance injection is selected, the enable switch signal S r is 0, the instruction signal I ref is subtracted from the sampled disturbance injection module output current I f to obtain the current deviation value ΔI. The current deviation value ΔI is multiplied by the gain index k pwm after the value obtained by the current inner loop PI control is limited to obtain the modulation signal u r3 . The obtained signal is subjected to PWM modulation to obtain the switch control signal when the current disturbance injection is performed, so as to control the conduction and turn-off of the power devices of the latter stage H-bridge.

[0035] In step 3), the transfer function of PI control is: wherein K p is the proportional coefficient of quasi-PI control, and the specific value is 0.0002; K i is the integral coefficient of PI control, and the specific value is 0.1. In step 7), K p is 20, and Ki is 0.5.

[0036] The transfer function of PI control when the current disturbance injection is performed is: wherein K p is the proportional coefficient of quasi-PI control, and the specific value is 20; K i is the integral coefficient of PI control, and the specific value is 0.5.

[0037] Figure 3 is the system voltage and current waveform of the 375V direct current power distribution system of the embodiment of the application after a disturbance sinusoidal voltage with a frequency of 10Hz and an amplitude of 30V is added.

[0038] Figure 4 is the system voltage and current waveform of the 375V direct current power distribution system of the embodiment of the application after a disturbance sinusoidal current with a frequency of 1000Hz and an amplitude of 30V is added.

[0039] Figure 5The figures show the simulation results of the Buck converter impedance model and impedance measurement according to the embodiment of the present invention. It can be seen from the figure that the theoretically derived impedance model and the impedance results simulated and measured using the embodiment of the present invention are in good agreement. The solid line is the theoretical model impedance result, and the circles are the simulated and measured impedance results of the embodiment of the present invention, which proves the effectiveness of the wide-band impedance measurement device and control method suitable for DC systems.

[0040] Example 2

[0041] Embodiment 2 of the present invention provides a control system corresponding to the above-mentioned embodiment 1, including a memory, a processor, and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method of the above-mentioned embodiment 1.

[0042] In some implementations, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory, such as at least one disk storage.

[0043] In other implementations, the processor may be a central processing unit (CPU), a digital signal processor (DSP), or other general-purpose processors, which are not limited here.

[0044] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0045] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A control method for a broadband impedance measurement device suitable for a DC power distribution system, characterized in that: The following steps are involved: S1, at the starting point of each sampling period, the DC side voltage U of the primary and secondary sides of the DAB converter in the sub-power module unit of the broadband impedance measurement device is measured. dc1 、U dc2 and the DC side voltage v of the subsequent H-bridge converter dc Take samples; S2, the voltage command signal U ref1 、U ref2 The voltage U on both sides of the primary and secondary sides of the DAB converter obtained by sampling dc1 、U dc2 The voltage error ΔU1 and ΔU2 are obtained by subtracting them; the voltage error ΔU1 and ΔU2 are controlled by the voltage outer loop PI and the values ​​obtained by the limit link and the gain index k pwm Multiply them to get the modulated signal u r1 、u r2 ; The modulated signal u r1 、u r2 Perform single phase shift modulation to obtain the duty cycle signal of the primary and secondary side switches in the DAB converter, and control the on and off of the DAB converter switches. When voltage disturbance is injected, the DC side voltage command value V dc Divide by the actual DC side voltage v of the single-phase H-bridge DC / AC converter dc , get the amplitude M of the modulated waveform a ; According to the frequency instruction ω, initial phase instruction and M a , the H-bridge modulation wave is obtained as t is the time, After bipolar SPWM multi-level modulation, the control signal of the subsequent H-bridge switch tube is obtained to control the on and off of the subsequent H-bridge power device; When the current disturbance is injected, the command signal I ref The current deviation value ΔI is obtained by subtracting the sampled output current If of the wide-band disturbance injection device; The current deviation value ΔI is obtained by the current inner loop PI control and the value is obtained by the limit link and the gain index k pwm Multiply them to get the modulated signal u r3 , the modulated signal u r3 Through PWM modulation, the switch control signal is obtained when the current disturbance is injected, thereby controlling the on and off of the subsequent H-bridge power device.

2. The control method of the broadband impedance measurement device applicable to a DC power distribution system according to claim 1, characterized in that: The transfer function of the voltage outer loop PI control is: where K p is the proportional coefficient of PI control, K i is the integral coefficient of PI control.

3. The control method of the broadband impedance measurement device applicable to a DC power distribution system according to claim 2, characterized in that: K p The value is 0.0002, K i The value is 0.

1.

4. The control method of the broadband impedance measurement device applicable to a DC power distribution system according to claim 1, characterized in that: The transfer function of the current inner loop PI control is: where K p1 is the proportional coefficient of PI control, K i1 is the integral coefficient of PI control.

5. The control method of the broadband impedance measurement device applicable to a DC power distribution system according to claim 4, characterized in that: K p1 The value is 20, K i1 The value is 0.

5.

6. A control system for a broadband impedance measurement device for a DC power distribution system, comprising a memory, a processor, and a computer program stored in the memory; characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 5.

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