Control method and system of broadband impedance measuring device suitable for direct current power distribution system

Abstract

The invention discloses a control method and system of a broadband impedance measurement device suitable for a DC power distribution system. The broadband impedance measurement device mainly comprises a signal disturbance injection unit, a voltage and current signal acquisition unit and a broadband impedance calculation unit. The signal disturbance injection unit is composed of a DC / DC / AC power sub-module and a filter circuit. Each DC / DC / AC power sub-module is composed of a DAB converter, a DC side capacitor and a SiC single-phase full bridge. A front-stage DAB converter of the signal disturbance injection device adopts outer ring voltage proportional integral single phase shift control, a rear-stage H bridge considers open-loop control of direct current side voltage fluctuation during voltage injection, and on and off of a single-phase full-bridge power device are controlled through bipolar SPWM modulation; and current inner loop proportional-integral control is adopted during current injection. According to the invention, the system has high reliability and faster dynamic response, and meets the requirement of broadband disturbance output impedance measurement in a DC system scene of large-scale optical storage new energy power generation equipment.

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 direct current power distribution system. Background Art

[0002] With the increasing number of DC loads such as large data centers, electric vehicle charging piles, and communication equipment, as well as the high proportion and large-capacity decentralized access of DC distributed power sources such as photovoltaics, the safe and stable operation of DC distribution systems has received extensive attention. Solar photovoltaic power generation is one of the most rapidly developing and promising renewable energy power generation industries. With the large-scale access of photovoltaic power generation, the increasing number of photovoltaic power generation equipment, and the rapid growth of loads such as power consumption equipment, the energy system presents the characteristics of high renewable energy penetration, high proportion of power electronic equipment, and high load growth rate ("three highs"), and the system faces challenges in terms of operation mode and reliability. At the same time, the large-scale new energy access DC distribution network system is a weak rotation inertia system dominated by power electronic equipment when it is independently operated. The system has strong time-varying characteristics and diverse operation modes. The lack of inertia of the DC distribution network, the random volatility of photovoltaics, and the unpredictability of loads will also bring great challenges to the stable control of system voltage and frequency. On the other hand, power electronic loads represented by charging piles need to be converted into electric energy through corresponding converters. These converters show constant power characteristics under closed-loop control, and present negative damping characteristics to the system, which will also bring 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 to analyze the oscillation problem of the grid-connected system of new energy converters. Its basic idea is to regard the converter and the AC power grid as two independent subsystems, use the impedance matrix to describe the external characteristics of the subsystem, and use the impedance ratio of the subsystem to judge the stability of the system. Since the system parameters and control parameters of existing new energy devices are difficult to obtain, it is difficult to carry out refined impedance modeling of new energy power generation equipment. Therefore, in view of the stability control problems caused by the large-scale access of new 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 view of the shortcomings of the existing technology, so as to meet the demand for accurate measurement of wide-band output impedance in the scenario of large-scale photovoltaic and energy storage access to DC systems.

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

[0006] S1, at the starting point of each sampling cycle, the DC side voltages Udc1 and Udc2 of the primary and secondary sides of the DAB converter and the DC side voltage v 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 is obtained by sampling dc1 , U dc2 The voltage error ΔU1 and ΔU2 are obtained by subtracting the voltage error ΔU1 and ΔU2; the voltage error ΔU1 and ΔU2 are obtained by the voltage outer loop PI control and the limit link and the gain index k pwm Multiply them to get the modulation 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 switch tubes in the DAB converter, and control the on and off of the DAB converter switch tubes;

[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, Through 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 controlled by the limit link and the gain index k pwm Multiply them to get the modulated signal u r3 , the modulated signal u r3 After 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 power grid side is small and easily affected by noise, making it impossible to accurately measure the impedance of the power grid; 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 impedance of the power grid, the current closed-loop control method can be used to measure the impedance of the power grid in parallel with the current injection system; when it is necessary to accurately measure the renewable energy power generation equipment, the voltage series injection system can be used to measure the renewable energy power generation device. Different disturbance injection control methods can also be selected according to different power grid impedance strengths to obtain accurate impedance characteristics of the DC power 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 wideband 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 refined 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 broadband 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 adding disturbance voltage 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 the disturbance current is added to the 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] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0023] Example 1

[0024] Figure 1 The figure shows a system structure diagram of a broadband impedance measurement device applicable to a DC power distribution system according to an embodiment of the present invention. The broadband impedance measurement device system applicable to 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 choose to inject a small disturbance voltage or a small disturbance current into the system, respond with a small disturbance current and a small disturbance voltage, and collect voltage and current to calculate 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 system consists of a DC / DC / AC power unit and a filter circuit. The DC / DC / AC power submodule consists of a DAB converter, a DC side capacitor and a SiC single-phase full bridge. The output is directly connected to the DC bus system to be tested through a filter circuit. In order to be able to be applied in practice, the device is equipped with a distribution cabinet and a switching cabinet, which can directly draw power from the 375V DC bus and is conducive to the input and removal of the device.

[0027] Figure 2 This is a block diagram of a control method for a broadband 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 is obtained by sampling dc1 , U dc2 Subtract the voltage and get the voltage errors ΔU1 and ΔU2.

[0030] 3) The voltage error ΔU1 and ΔU2 are obtained by the voltage outer loop PI control and then passed through the limit link and the gain index k pwm Multiplying them gives the modulated signal u r1 、u r2 .

[0031] 4) The modulation 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 switches of the DAB converter.

[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 DC voltage command by the actual value as the modulation factor, the active power output of the H-bridge can be adjusted during the DC voltage fluctuation, thereby improving the dynamic performance of the voltage disturbance injection device.

[0033] 6) According to the frequency instruction ω, initial phase instruction and M a , the H-bridge modulation waves are t is the time, Through bipolar SPWM multi-level modulation, the subsequent H-bridge switch control signals S1, S2, S3, and S4 are obtained, thereby controlling the on and off of the subsequent H-bridge power devices.

[0034] 7) When selecting current disturbance injection, enable the switch signal S r =0, the command signal I ref The disturbance injection module output current I f The current deviation value ΔI is obtained by subtracting the current deviation value ΔI from the current inner loop PI control value. After the current deviation value ΔI passes through the limiting link, it is combined with the gain index k pwm Multiplying them gives the modulated signal u r3 The obtained signal is modulated by PWM to obtain the switch control signal when the current disturbance is injected, thereby controlling the on and off of the subsequent H-bridge power device.

[0035] In step 3), the transfer function of PI control is: Where K p The specific value of the proportional coefficient of quasi-PI control is 0.0002; K i is the integral coefficient of PI control, and its 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 current disturbance is injected is: Where K p The specific value of the proportional coefficient of quasi-PI control is 20; K i is the integral coefficient of PI control, and its specific value is 0.5.

[0037] Figure 3 The system voltage and current waveforms after a disturbed sinusoidal voltage with a frequency of 10 Hz and an amplitude of 30 V is added to the 375 V DC power distribution system of the embodiment of the present invention.

[0038] Figure 4 The system voltage and current waveforms after adding a disturbed sinusoidal current with a frequency of 1000 Hz and an amplitude of 30 V to the 375 V DC power distribution system of the embodiment of the present invention.

[0039] Figure 5The simulation results of the impedance model and impedance measurement of the Buck converter in the embodiment of the present invention. It can be seen from the figure that the theoretically derived impedance model and the impedance result simulated and measured by the embodiment of the present invention can be well consistent. The solid line is the impedance result of the theoretical model, and the circle is the impedance result simulated and measured by 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 memory.

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

[0044] Although the preferred embodiments of the present application have been described, those skilled in the art may make other 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 falling within the scope of the present application.

[0045] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also 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 is obtained by sampling dc1 , U dc2 The voltage error ΔU1 and ΔU2 are obtained by subtracting the voltage error ΔU1 and ΔU2; the voltage error ΔU1 and ΔU2 are obtained by the voltage outer loop PI control and 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 switch tubes in the DAB converter, and control the on and off of the DAB converter switch tubes; 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, Through 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 Subtract the sampled output current If from the wide-band disturbance injection device to obtain a current deviation value ΔI; 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 After 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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