Control system and method for suppressing specific harmonic waves in direct-current power transmission

Abstract

The invention relates to a control system and method for restraining specific harmonic waves through direct current transmission, and the method comprises the steps that a converter station controls a given value of valve control main control equipment in each period, and the valve control main control equipment converts the given values of the current period and the last period into two paths of input signals needed by bridge arm control equipment; the bridge arm control equipment calculates and generates multiple paths of multi-packet action signals with the period smaller than that of the two paths of input signals and the precision higher than that of the two paths of input signals according to the two paths of input signals, and the multiple paths of signals determine an action information packet of the valve unit in a PWM (Pulse Width Modulation) or nearest level approximation mode; the action information packet comprises an action command needing to be executed by the valve unit and time information for executing the command, and the valve unit executes the command according to the action information packet; the output precision of the valve unit is effectively improved, so that specific harmonic waves are suppressed, and the problem that specific high-frequency harmonic waves are introduced due to a system control period is solved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a control system and method for suppressing specific harmonics in direct current transmission. Background Art

[0002] In recent years, modular multilevel converters have developed rapidly in flexible DC transmission technology, and the control of flexible DC transmission has become more and more mature. Generally, flexible DC transmission control can be divided into four layers, namely system-level control, pole control, converter-level control and valve control. Valve control generates sub-module semiconductor switch control signals based on physical quantities such as bridge arm modulation waves, capacitor voltage, bridge arm current, etc. generated by converter-level control. Since the control cycle of the valve control device in the current flexible DC transmission control is usually 50 microseconds, it is easy to cause 20KHz harmonics. Such specific harmonics are easy to cause damage to electrical equipment in the flexible DC system, such as insulators, insulating bushings, etc. In order to ensure the safety and stability of the flexible DC transmission system, the problem of specific high-frequency harmonics introduced by the control cycle needs to be solved urgently.

[0003] A Chinese patent with publication number CN113258555B discloses a harmonic resonance suppression method and system for a flexible direct current transmission system, comprising: obtaining a three-phase current signal and sending it to an analog-to-digital converter to obtain a current digital signal; performing Hanning windowed Fourier transform processing on the current digital signal to obtain resonance information; constructing an ideal same-frequency positive-sequence three-phase voltage according to the resonance information; performing phase-locking processing on the same-frequency positive-sequence three-phase voltage to obtain a phase-locking result; performing proportional-integral control on a specific harmonic component of the current digital signal based on the phase-locking result to obtain a preliminary voltage reference value; superimposing the preliminary voltage reference value with the voltage reference value generated by the current inner loop to obtain a final voltage reference value; avoiding the suppression failure problem caused by changes in the system operation mode in the existing suppression method; but the present invention does not solve the harmonic problem caused by a specific control cycle. Summary of the invention

[0004] The present invention provides a control system and method for suppressing specific harmonics in direct current transmission, which effectively improves the output accuracy of valve units, thereby suppressing specific harmonics and solving the problem of introducing specific high-frequency harmonics due to system control cycles.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A control system for suppressing specific harmonics in direct current transmission, comprising a converter station, a valve control main control device, a bridge arm control device and a valve unit, wherein the output end of the converter station is connected to the input end of the valve control main control device, the output end of the valve control main control device is connected to the input end of the bridge arm control device, and the output end of the bridge arm control device is connected to the input end of the valve unit;

[0007] The converter station is used to generate a given value required for adjustment by the valve control main control device;

[0008] The valve control master device is used to receive a given value for each cycle of the converter station control;

[0009] The bridge arm control device is used to generate multiple channels and multiple groups of action signals;

[0010] The valve unit is used to execute the action information command issued by the bridge arm control device.

[0011] Furthermore, the valve control main control device and the bridge arm control device are collectively referred to as a valve control system, and both use DSP or FPGA chips.

[0012] Furthermore, the valve unit includes a plurality of power units, and the power units include a full-bridge power unit and a half-bridge power unit.

[0013] A control method for suppressing specific harmonics in direct current transmission, wherein the converter station controls the given value of each cycle of a valve control main control device, the valve control main control device converts the given values ​​of the current cycle and the previous cycle into two input signals required by a bridge arm control device, the bridge arm control device calculates and generates multiple groups of action signals with a cycle smaller than the two input signals and a higher precision than the two input signals according to the two input signals, the multiple signals are subjected to PWM modulation or the nearest level approximation method to determine the action information package of the valve unit, the action information package includes the action instruction to be executed by the valve unit and the time information for executing the instruction, and the valve unit executes the command according to the action information package.

[0014] Furthermore, the given value is a voltage parameter, and the voltage parameter includes a voltage value that the valve unit needs to output or a ratio of the voltage value that the valve unit needs to output to a DC voltage of the power transmission system.

[0015] Furthermore, the two input signals required by the bridge arm control device are the number of power units required to be invested in the valve unit, which are calculated by the valve control main control device according to the voltage parameters and the average value of the capacitor voltage.

[0016] Furthermore, the calculation generation cycle of the multi-channel and multi-group action signals is shorter than that of the two-channel input signals and the accuracy is higher than that of the two-channel input signals. The calculation is performed using a numerical processing algorithm.

[0017] Furthermore, the action instruction includes the action state of the power unit switch, which is the switch state of outputting positive level, negative level, and zero level, and the time information for executing the instruction is the time information of the power switch action.

[0018] Furthermore, the bridge arm control device sends the calculated and generated multi-channel signals to the valve unit at one time in a packaging manner.

[0019] Furthermore, the multi-channel signal includes multiple channels and multiple groups of action signals, wherein the multiple channels are multiple power units and the multiple groups are different time periods.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The communication content from the valve control main control device to the bridge arm control device includes not only the number of modules put into operation in the current cycle, but also the number of modules put into operation in the previous cycle. The bridge arm control device generates multiple groups of action information packets with shorter cycles and higher precision through interpolation or prediction methods based on the signals of the number of modules put into operation on two channels. The action information packets include the action instructions that the valve unit needs to execute and the time information for executing the instructions. This will effectively improve the output accuracy of the valve unit, thereby suppressing specific harmonics and solving the problem of introducing specific high-frequency harmonics due to the system control cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the system of the present invention.

[0023] Figure 2 It is a flow chart of the method of the present invention.

[0024] Figure 3 It is a schematic diagram of the control flow described in an embodiment of the present invention.

[0025] Figure 4 It is a schematic diagram of the total output voltage of the valve unit described in the embodiment of the present invention. DETAILED DESCRIPTION

[0026] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0027] See Figure 1 , is a structural diagram of the system of the present invention. A control system for suppressing specific harmonics in direct current transmission of the present invention comprises a converter station, a valve control main control device, a bridge arm control device and a valve unit, wherein the output end of the converter station is connected to the input end of the valve control main control device, the output end of the valve control main control device is connected to the input end of the bridge arm control device, and the output end of the bridge arm control device is connected to the input end of the valve unit;

[0028] The converter station is used to generate a given value required for adjustment by the valve control main control device;

[0029] The valve control master device is used to receive a given value for each cycle of the converter station control;

[0030] The bridge arm control device is used to generate multiple channels and multiple groups of action signals;

[0031] The valve unit is used to execute the action information command issued by the bridge arm control device and perform actions according to the action signal packet.

[0032] The valve control main control device and the bridge arm control device are collectively referred to as the valve control system, which is composed of chips such as DSP and FPGA; the control cycle of the valve control main control device is consistent with that of the converter station control, which is 50 microseconds.

[0033] The valve unit includes a plurality of power units, and the power units include a full-bridge power unit and a half-bridge power unit.

[0034] See Figure 2 , a control method for suppressing specific harmonics in direct current transmission, wherein the control device of the converter station receives commands from the power grid, such as corresponding active and reactive power instructions, or raising the direct current voltage, etc.; according to its control algorithm, a set value is calculated for each valve control main device, such as the output voltage value of the current valve unit;

[0035] The given value of each cycle of the converter station control valve control main control device is a voltage parameter, and the voltage parameter is the voltage value required to be output by the valve unit or the ratio of the voltage value required to be output by the valve unit to the DC voltage of the power transmission system;

[0036] The valve control main control device calculates the number of modules required to be put into operation in the valve unit according to the voltage parameters and the average value of the capacitor voltage, and uses the number of modules calculated in the previous cycle as the input of the bridge arm control device.

[0037] The bridge arm control device calculates the number of input modules with a shorter period and higher precision than the two input signals through a numerical processing algorithm based on the two input signals, and then calculates multiple groups of action information packets through a PWM modulation algorithm or a nearest level approximation method. The action information packet is the action instruction that the valve unit needs to execute and the time information for executing the instruction. Since the valve unit is composed of multiple power units, the bridge arm control device ultimately generates multiple groups of action signal packets.

[0038] The valve unit executes the command according to the action information packet.

[0039] The action signal package consists of an action instruction and the time information for executing the instruction. The action instruction refers to the positive level, negative level or zero level of the power unit action output. After the valve unit receives the action signal package through the optical fiber, it executes the action instruction according to the action signal package, thereby finally realizing the set value of the converter station.

[0040] See Figure 3 The power module in the figure is the power unit mentioned above, and the control period of the converter control device is t n+1 -t n =50μs, each cycle will be given value Transmitted to the valve control master device; the valve control master device calculates the number of modules required for the valve unit in the current cycle through its own algorithm And the number of input modules calculated in the previous cycle Together they serve as the input of the bridge arm control device; the bridge arm control device generates multiple input modules with shorter cycles and higher precision by interpolation method ( M takes value as required), and then calculates the multiple groups of action information packets required by the valve unit to meet the modulation signal through PWM modulation algorithm or the nearest level approximation method. For example, the multiple groups of action information packets of 1# power unit are as follows:

[0041]

[0042] Among them, (S 1tn ,S 1t(n+k) ,…S 1t(n+M*k) ) is the action instruction information of 1#;

[0043] (S 1time_tn ,S 1time_t(n+k) ,…,S 1time_t(n+M*k) ) is the action instruction time information of 1#.

[0044] The valve unit is composed of a number of power units, so the valve unit requires multiple channels and groups of action information packets. Ultimately, each power unit performs an action according to the corresponding action instruction information and action instruction time information.

[0045] See Figure 2 The system includes a converter station control device and a valve control master device. Each bridge arm control device controls each bridge arm. Each bridge arm includes N power units. When the valve control master device receives a given value from the converter station control device, it is assumed that the given value changes continuously over time and increases linearly and smoothly. The total output voltage is required to increase linearly over time, such as Figure 4 As shown, in (t n ,t n+1 ) interval, the bridge arm control device sends multiple groups of action signal packets to the valve unit, for example, at t n+k At this moment, each power unit responds to multiple action information packets (S 1t(n+k) ,S 1time_t(n+k) )、(S 2t(n+k) ,S 2time_t(n+k) )…(S Nt(n+k) ,S Ntime_t(n+k) ) executes the action, requiring the N# power unit to execute the action according to the action instruction time information S Ntime_t(n+k) Execute the output positive level action, the valve unit output total voltage result is as follows Figure 4 As shown, it satisfies the input requirements of the converter station control equipment very well.

[0046] Among them, S 1t(n+k) , S 2t(n+k) …S Nt(n+k)Action command information for power units 1# to N#;

[0047] S 1time_t(n+k) , S 2time_t(n+k) …S Ntime_t(n+k) It is the action instruction time information of power units 1# to N#.

[0048] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A control system for suppressing specific harmonics in direct current transmission, characterized in that: It includes a converter station, a valve control main control device, a bridge arm control device and a valve unit, wherein the output end of the converter station is connected to the input end of the valve control main control device, the output end of the valve control main control device is connected to the input end of the bridge arm control device, and the output end of the bridge arm control device is connected to the input end of the valve unit; The converter station is used to generate a given value required for adjustment by the valve control main control device; The valve control master device is used to receive a given value for each cycle of the converter station control; The bridge arm control device is used to generate multiple channels and multiple groups of action signals; The valve unit is used to execute the action information command issued by the bridge arm control device.

2. A control system for suppressing specific harmonics in direct current transmission according to claim 1, characterized in that: The valve control main control device and the bridge arm control device are collectively referred to as a valve control system, and both use DSP or FPGA chips.

3. A control system for suppressing specific harmonics in direct current transmission according to claim 1, characterized in that: The valve unit includes a plurality of power units, and the power units include a full-bridge power unit and a half-bridge power unit.

4. The control method of a control system for suppressing specific harmonics in direct current transmission according to any one of claims 1 to 3, characterized in that: The converter station controls the given value of each cycle of the valve control main control device, and the valve control main control device converts the given values ​​of the current cycle and the previous cycle into two input signals required by the bridge arm control device. The bridge arm control device calculates and generates multiple groups of action signals with a cycle smaller than the two input signals and a higher accuracy than the two input signals based on the two input signals. The multiple signals are subjected to PWM modulation or the nearest level approximation method to determine the action information package of the valve unit. The action information package includes the action instruction that the valve unit needs to execute and the time information for executing the instruction. The valve unit executes the command according to the action information package.

5. A control method for suppressing specific harmonics in direct current transmission according to claim 4, characterized in that: The given value is a voltage parameter, and the voltage parameter includes a voltage value that the valve unit needs to output or a ratio of a voltage value that the valve unit needs to output to a DC voltage of a power transmission system.

6. A control method for suppressing specific harmonics in direct current transmission according to claim 4, characterized in that: The two input signals required by the bridge arm control device are the number of power units required to be invested in the valve unit, which is calculated by the valve control main control device based on the voltage parameters and the average value of the capacitor voltage.

7. A control method for suppressing specific harmonics in direct current transmission according to claim 4, characterized in that: The calculation generation cycle of the multi-channel and multi-group action signal signals is shorter than that of the two-channel input signals and the accuracy is higher than that of the two-channel input signals. The calculation is performed using a numerical processing algorithm.

8. A control method for suppressing specific harmonics in direct current transmission according to claim 4, characterized in that: The action instruction includes the action state of the power unit switch, which is the switch state of outputting positive level, negative level and zero level, and the time information of executing the instruction is the time information of the power switch action.

9. A control method for suppressing specific harmonics in direct current transmission according to claim 4, characterized in that: The bridge arm control device sends the calculated multi-channel signals to the valve unit at one time in a packaging manner.

10. A control method for suppressing specific harmonics in direct current transmission according to claim 4, characterized in that: The multiple paths and multiple groups of action signals, wherein the multiple paths are multiple power units, and the multiple groups are different time periods.

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