Converting control device of frequency converter

Abstract

The invention discloses a variable current control device of a frequency converter. The variable current control device comprises a main circuit topology and a system-level control module, the system-level control module comprises a power calculation module, a voltage generation module, an active power filter module and a PWM generation module; the power calculation module is used for calculating the reactive power of the frequency converter according to the sampling voltage at the common coupling point and the three-phase compensation current generated by the frequency converter; the voltage generation module is used for performing power control according to reactive power and direct-current side sampling voltage of the frequency converter and generating a three-phase voltage signal; the active power filter module is used for performing harmonic compensation based on the three-phase voltage signal to obtain a modulation voltage signal; and the PWM generation module is used for generating a pulse width modulation control signal according to the modulation voltage signal and inputting the pulse width modulation control signal into the H-bridge circuit. Power control is performed through the system-level control module to realize reactive power compensation, and harmonic compensation is performed on the main circuit topology, so that the electric energy quality of the power supply is improved.

Description

Technical Field

[0001] The present application relates to the field of power electronic control technology, and more specifically, to a current conversion control device for a frequency converter. Background Art

[0002] In the large-scale connection between the silk-making workshop and the power grid, the output power of the silk-making workshop needs to be connected to the AC power grid through a frequency converter, but the output current of the frequency converter usually contains harmonics. In addition, there are a large number of power electronic conversion devices in the silk-making workshop. The interaction between the devices and the impedance of each device and the line may cause a series of harmonic resonance problems, further threatening the stable operation of the system. Summary of the invention

[0003] The present application provides a current conversion control device for a frequency converter, which realizes reactive power compensation by performing power control through a system-level control module, and simultaneously performs harmonic compensation on the main circuit topology, thereby greatly improving the grid harmonics and power factor, thereby improving the power quality of the power supply.

[0004] The present application provides a current conversion control device for a frequency converter, including a main circuit topology and a system-level control module;

[0005] The main circuit topology includes a frequency converter, a main line of a power grid, a connection line between the frequency converter and the power grid, and a connection line between the power grid and a load, and the frequency converter includes an H-bridge circuit;

[0006] The system-level control module includes a power calculation module, a voltage generation module, an active power filter module and a PWM generation module;

[0007] The power calculation module is used to calculate the reactive power of the inverter according to the sampled voltage at the common coupling point and the three-phase compensation current generated by the inverter;

[0008] The voltage generation module is used to perform power control according to reactive power and the DC side sampling voltage of the inverter to generate a three-phase voltage signal;

[0009] The active power filter module is used to perform harmonic compensation based on the three-phase voltage signal to obtain a modulated voltage signal;

[0010] The PWM generation module is used to generate a pulse width modulation control signal according to the modulation voltage signal and input it into the H-bridge circuit.

[0011] Preferably, the voltage generation module includes a reactive power control module, an active power control module and a voltage signal generation module;

[0012] The reactive power control module is used to calculate the electromotive force amplitude based on the reactive power reference signal and reactive power of the inverter;

[0013] The active power control module is used to calculate the phase angle according to the DC bus voltage reference signal of the inverter and the DC side sampling voltage;

[0014] The voltage signal generating module is used to obtain three-phase voltage signals according to the electromotive force amplitude and phase angle.

[0015] Preferably, the active power filter module comprises a Park conversion module, a voltage control module and an inverse Park conversion module.

[0016] Preferably, the active power filter module further includes a current control module.

[0017] Preferably, the input signal of the voltage control module includes a d-axis voltage reference signal and a q-axis voltage reference signal obtained by Park transformation of the three-phase voltage signal and a d-axis voltage component and a q-axis voltage component obtained by Park transformation of the sampled voltage at the common coupling point, and the output signal is a d-axis fundamental current reference signal and a q-axis fundamental current reference signal.

[0018] Preferably, the input signals of the current control module are the d-axis fundamental current reference signal, the q-axis fundamental current reference signal, the d-axis harmonic current signal and the q-axis harmonic current signal to be compensated, and the d-axis compensation current component and the q-axis compensation current component obtained by Park transformation of the three-phase compensation current generated by the inverter.

[0019] Preferably, the reactive power control module calculates the electromotive force amplitude using a droop control principle.

[0020] Preferably, the voltage control module calculates the d-axis fundamental current reference signal and the q-axis fundamental current reference signal using a proportional-integral control principle.

[0021] Preferably, the final input signal of the current control module includes the difference between the sum of the d-axis fundamental current reference signal and the d-axis harmonic current signal and the d-axis compensation current component and the difference between the sum of the q-axis fundamental current reference signal and the q-axis harmonic current signal and the q-axis compensation current component.

[0022] Preferably, obtaining the d-axis harmonic current signal and the q-axis harmonic current signal that need to be compensated specifically includes:

[0023] Perform Park transformation on the load current of the inverter to obtain the d-axis load current component and the q-axis load current component;

[0024] Inputting the d-axis load current component and the q-axis load current component into a low-pass filter respectively to obtain a d-axis filtered current component and a q-axis filtered current component;

[0025] The difference between the d-axis load current component and the d-axis filter current component is used as the d-axis harmonic current signal, and the difference between the q-axis load current component and the q-axis filter current component is used as the q-axis harmonic current signal.

[0026] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0028] Figure 1 A system structure diagram of the current conversion control device of the frequency converter provided in this application;

[0029] Figure 2 A schematic diagram of an active power control module provided in this application;

[0030] Figure 3 A schematic diagram of a reactive power control module provided for this application;

[0031] Figure 4 A schematic diagram of a voltage control module provided in this application;

[0032] Figure 5 A schematic diagram of obtaining a harmonic current signal that needs to be compensated provided in this application;

[0033] Figure 6 A schematic diagram of a current control module provided in this application;

[0034] Figure 7 The voltage and current waveforms of phase A in Comparative Example 1 provided in this application;

[0035] Figure 8 The voltage and current waveforms of phase A in Comparative Example II provided in this application;

[0036] Fig. 9 The voltage and current waveforms of phase A in Comparative Example III provided in this application;

[0037] Fig.10 In Comparative Example IV provided in the present application, the reactive power waveform of the inverter when the grid voltage amplitude and frequency fluctuate. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0039] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0040] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0041] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0042] The present application provides a current conversion control device for a frequency converter, which realizes reactive power compensation by performing power control through a system-level control module, and simultaneously performs harmonic compensation on the main circuit topology, thereby greatly improving the grid harmonics and power factor, thereby improving the power quality of the power supply.

[0043] like Figure 1 As shown, the inverter current control device provided in the present application includes a main circuit topology and a system-level control module.

[0044] The main circuit topology includes a frequency converter 140, a main line 110 of a power grid, a connection line 130 between the frequency converter and the power grid, and a connection line 120 between the power grid and a load. The frequency converter 140 includes an H-bridge circuit and a DC side capacitor C dc , the DC side sampling voltage is v dc The connection line 130 between the inverter and the power grid includes the inverter filter inductor L f , equivalent resistance R f And the inverter side line impedance Z line2 Through this connection line, the three-phase compensation current generated by the inverter is i cabc The main grid line 110 includes a grid line impedance Z g , the three-phase current on the grid side is i sabc , the three-phase grid voltage is v gabc The connection line 120 between the grid and the load includes a load-side line impedance Z line1 , bridge full-wave rectifier, load inductor L load and load R load , the load current is i labc The sampling voltage at the common coupling point (PCC) of the connection line 120 between the grid and the load and the connection line 130 between the inverter and the grid is v abc .

[0045] The system-level control module includes a power calculation module 150 , a voltage generation module 160 , an active power filter (APF) module 170 and a PWM generation module 180 .

[0046] The power calculation module 150 is used to calculate the power of the sampled voltage v at the common coupling point according to the sampling voltage v abc And the three-phase compensation current i generated by the inverter cabc Calculate the inverter's reactive power Q c .

[0047] The voltage generating module 160 is used to generate a voltage according to the reactive power Q c and the DC side sampling voltage v of the inverter dc Perform power control and generate three-phase voltage signals abc .

[0048] The active power filter module 170 is used to generate a three-phase voltage signal based on the three-phase voltage signal e abc Perform harmonic compensation to obtain a modulated voltage signal.

[0049] The PWM generation module 180 is used to generate a pulse width modulation control signal according to the modulation voltage signal, and input the pulse width modulation control signal into the H-bridge circuit.

[0050] As an embodiment, the voltage generating module 160 includes a reactive power control module, an active power control module and a voltage signal generating module.

[0051] The reactive power control module is used to control the reactive power reference signal Q of the inverter. cr and reactive power Q c Calculate the magnitude of the electromotive force E.

[0052] As an embodiment, the reactive power control module uses the droop control principle to calculate the electromotive force amplitude. q It is designed based on the relationship between the change in reactive power output by the inverter and the change in the AC bus voltage of the power grid. Based on the droop principle, the reactive power of the inverter can be automatically adjusted according to the change in the system AC bus voltage, realizing the reactive power compensation function of SVG (Static Var Generator) and providing voltage support for the system, such as Figure 3 As shown:

[0053] E=(Q cr -Q c )×D q +V N (1)

[0054] Among them, V N is the given value of AC voltage.

[0055] SVG emits or absorbs reactive power through a three-phase bridge circuit, and has the advantages of fast response time and bidirectional continuous reactive power regulation.

[0056] The active power control module is used to control the DC bus voltage reference signal v of the inverter. dcr And the DC side sampling voltage v dc Calculate the phase angle θ.

[0057] According to the energy characteristics of the DC bus capacitor, it can be concluded that

[0058]

[0059] Among them, P in and P out They are respectively the active power input to the DC side of the inverter and the active power injected into the grid by the inverter; G m is the virtual conductance.

[0060] The rotor equation of a conventional synchronous generator is called

[0061]

[0062] Where J represents the moment of inertia of the synchronous generator; ω represents the angular velocity of rotation; P′ in and P′ our Represent mechanical power input and electromagnetic power output respectively; D p Represents the damping factor.

[0063] By comparing equations (2) and (3), the charging and discharging process of the DC bus capacitor can be compared with the acceleration and deceleration process of the synchronous generator (i.e., P in -P our =P′ in -P′ out The charging and discharging of the DC capacitor achieves active power balance between the DC and AC sides of the inverter while tracking the frequency and phase of the grid. The combination of equations (2) and (3) produces:

[0064]

[0065] Formula (4) describes the relationship between the change of DC bus voltage and the change of angular frequency. Since the change of DC bus voltage reflects the change of inverter active power, the expression of the active power control module of the grid-forming inverter can be obtained according to formula (4), as follows: Figure 2 As shown:

[0066]

[0067] Among them, s represents the frequency domain factor, ω′ represents the angular frequency of the inverter, θ represents the phase angle of the inverter, ω N Represents a given angular frequency, which is consistent with the angular frequency of the power grid.

[0068] The voltage signal generation module is used to obtain the three-phase voltage signal e according to the electromotive force amplitude E and the phase angle θ. abc .

[0069] As an embodiment, the active power filter module includes a Park transformation module, a voltage control module and an inverse Park transformation module.

[0070] The Park transformation module is used to convert the three-phase voltage signal abc Transform to obtain the d-axis voltage reference signal v dr and the q-axis voltage reference signal v qr .

[0071] As an embodiment, the input signal of the voltage control module includes a d-axis voltage reference signal v dr and the q-axis voltage reference signal v qr And the sampled voltage v at the common coupling point abc The d-axis voltage component v obtained by Park transformation d and the q-axis voltage component v q , the output signal is the d-axis fundamental current reference signal i dr and q-axis fundamental current reference signal i qr .

[0072] As an embodiment, the voltage control module uses the proportional integral control principle to calculate the d-axis fundamental current reference signal i dr and q-axis fundamental current reference signal i qr , expressed as:

[0073]

[0074] Among them, K pv and K iv are the proportional coefficient and integral coefficient of the voltage controller, respectively. Figure 4 shown.

[0075] Voltage detection type active power filter. By detecting the harmonic voltage of the power grid and controlling the conductivity characteristics of the active power filter at the harmonic frequency, the purpose of enhancing damping and suppressing resonance is achieved.

[0076] Preferably, the active power filter module 170 further includes a current control module.

[0077] As an embodiment, the input signal of the current control module is the d-axis fundamental current reference signal i dr, q-axis fundamental current reference signal i qr 、The d-axis harmonic current signal i that needs to be compensated ldh and q-axis harmonic current signal i lqh And the three-phase compensation current i generated by the inverter cabc The d-axis compensation current component i obtained by Park transformation cd and the q-axis compensation current component i cq .

[0078] Therefore, the final input signal of the current control module includes the d-axis fundamental current reference signal i dr and d-axis harmonic current signal i ldh The sum of the d-axis compensation current component i cd The difference dcr And the q-axis fundamental current reference signal i qr and q-axis harmonic current signal i lqh The sum of the q-axis compensation current component i cq The difference qcr ,Right now

[0079]

[0080] The transfer function H of the current controller i (s) is described as formula (8), whose input is the above final input signal i dcr and i qcr , the output is the d-axis modulation voltage signal v md and the q-axis modulation voltage signal v mq ,like Figure 6 As shown:

[0081]

[0082] Among them, K pi and K ii They are the proportional coefficient and integral coefficient of the proportional-integral controller of the current control module; K 6k is the resonant coefficient of the resonant controller, ω 6k is the resonant angular frequency, ω 6k =6k*ω N .

[0083] In order to obtain the d-axis modulation voltage signal v md and the q-axis modulation voltage signal v mq After that, it is transformed into a three-phase modulated voltage signal through the inverse Park transformation module and input into the H-bridge circuit to realize the current conversion control of the inverter.

[0084] As an example, Figure 5 As shown, the d-axis harmonic current signal i that needs to be compensated is obtained. ldhand q-axis harmonic current signal i lqh , including:

[0085] The load current i of the inverter labc Perform Park transformation to obtain the d-axis load current component i ld and the q-axis load current component i lq .

[0086] The d-axis load current component i ld and the q-axis load current component i lq Input the low-pass filter respectively to obtain the d-axis filtered current component i ld0 and the q-axis filtered current component i lq0 .

[0087] The d-axis load current component i ld and the d-axis filtered current component i ld0 The difference is taken as the d-axis harmonic current signal i ldh , the q-axis load current component i lq and the q-axis filtered current component i lq0 The difference is taken as the q-axis harmonic current signal i lqh .

[0088] The above-mentioned current control module mainly detects the harmonic current on the load side and generates equal and opposite currents at the load harmonic frequency to offset the impact of the load harmonic current on the power grid. It is also called a current sensing active power filter.

[0089] Both current detection type and voltage detection type active filters can achieve harmonic compensation by controlling a three-phase bridge circuit. As mentioned above, SVG can also adopt a three-phase bridge circuit topology. Therefore, the present application uses the same topology to integrate SVG and APF together to achieve grid-connected control, greatly improving the grid harmonics and power factor of the inverter, thereby improving the power quality of the workshop power supply.

[0090] In order to verify the harmonic control, reactive power compensation and resonance suppression functions of the designed SVG+APF integrated grid-connected inverter, the following cases are selected for Matlab simulation comparison.

[0091] Comparative Example I: The inverter adopts traditional APF control.

[0092] Comparative Example II: The inverter adopts traditional grid-following SVG control.

[0093] Comparative Example III: The frequency converter adopts the grid-connected control with SVG and APF functions of the present application.

[0094] Comparative Example IV: The inverter is controlled by following the grid and building the grid respectively, and the system does not contain nonlinear loads.

[0095] Please see attached Figure 7 , when the inverter is controlled by conventional APF, Figure 7 The collected A-phase voltage and current waveforms are given, where the waveforms from top to bottom are the voltage at the PCC, the load current, the inverter current, and the grid current. In this case, the normal PWM signal of the inverter is enabled at 0.1s, that is, the APF function is activated. It can be seen from the figure that before the APF function is enabled, the grid current waveform is the same as the load current waveform before 0.1s, and the inverter output current is 0, so all the harmonic currents of the load flow into the grid; when the APF function is enabled, all the harmonic currents of the load are offset by the inverter, and the harmonic content of the grid current waveform is close to 0, which proves that the parallel inverter has a good harmonic control function. However, by comparing the phases of the PCC voltage and the grid current, it can be found that the grid current phase lags behind the PCC voltage, which means that the reactive power required by the load is completely provided by the grid, and the APF does not have a reactive power compensation function.

[0096] Please see attached Figure 8 , when the inverter is controlled by a traditional grid following SVG, Figure 8 The voltage and current waveforms of phase A collected by the system are given. Comparing the phases of the PCC voltage and the grid current, it can be seen that the two phases are basically the same. However, there are harmonics in the grid current, indicating that the parallel inverter can only achieve the function of reactive power compensation.

[0097] Please see attached Fig. 9 When APF and SVG functions are combined in a network control, Fig. 9 The A-phase voltage and current waveforms collected by the system are given. It can be seen that the parallel inverter almost completely compensates for the harmonic current of the load, making the grid current waveform approximately sinusoidal, indicating that the designed parallel inverter realizes the function of APF. In addition, the phase difference between the grid current and the PCC voltage is almost zero, which indicates that the reactive power required by the load can be provided by the parallel inverter, indicating that the designed parallel inverter realizes the function of SVG.

[0098] Fig.10 The waveform of the inverter output reactive power is given when the frequency and amplitude of the grid voltage change. Fig.10 It can be seen that the reactive power changes significantly with the voltage amplitude, which is similar to the characteristics of the synchronous generator, indicating that the inverter has a voltage active support capability similar to that of the synchronous generator and realizes the function of grid-connected control.

[0099] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A current conversion control device for a frequency converter, characterized in that: Including main circuit topology and system-level control module; The main circuit topology includes a frequency converter, a main line of a power grid, a connection line between the frequency converter and the power grid, and a connection line between the power grid and a load, wherein the frequency converter includes an H-bridge circuit; The system-level control module includes a power calculation module, a voltage generation module, an active power filter module and a PWM generation module; The power calculation module is used to calculate the reactive power of the frequency converter according to the sampled voltage at the common coupling point and the three-phase compensation current generated by the frequency converter; The voltage generation module is used to perform power control according to the reactive power and the DC side sampling voltage of the inverter to generate a three-phase voltage signal; The active power filter module is used to perform harmonic compensation based on the three-phase voltage signal to obtain a modulated voltage signal; The PWM generation module is used to generate a pulse width modulation control signal according to the modulation voltage signal and input the pulse width modulation control signal into the H-bridge circuit.

2. The current conversion control device of the frequency converter according to claim 1, characterized in that: The voltage generation module includes a reactive power control module, an active power control module and a voltage signal generation module; The reactive power control module is used to calculate the electromotive force amplitude according to the reactive power reference signal and reactive power of the frequency converter; The active power control module is used to calculate the phase angle according to the DC bus voltage reference signal and the DC side sampling voltage of the inverter; The voltage signal generating module is used to obtain the three-phase voltage signal according to the electromotive force amplitude and the phase angle.

3. The current conversion control device of the frequency converter according to claim 1, characterized in that: The active power filter module includes a Park conversion module, a voltage control module and an inverse Park conversion module.

4. The current conversion control device of the frequency converter according to claim 3, characterized in that: The active power filter module also includes a current control module.

5. The current conversion control device of the frequency converter according to claim 4, characterized in that: The input signal of the voltage control module includes a d-axis voltage reference signal and a q-axis voltage reference signal obtained by Park transformation of the three-phase voltage signal, and a d-axis voltage component and a q-axis voltage component obtained by Park transformation of the sampled voltage at the common coupling point, and the output signal is a d-axis fundamental current reference signal and a q-axis fundamental current reference signal.

6. The current conversion control device of the frequency converter according to claim 5, characterized in that: The input signals of the current control module are the d-axis fundamental current reference signal, the q-axis fundamental current reference signal, the d-axis harmonic current signal and the q-axis harmonic current signal to be compensated, and the d-axis compensation current component and the q-axis compensation current component obtained by Park transformation of the three-phase compensation current generated by the inverter.

7. The current conversion control device of the frequency converter according to claim 2, characterized in that: The reactive power control module calculates the electromotive force amplitude using the droop control principle.

8. The current conversion control device of the frequency converter according to claim 5, characterized in that: The voltage control module calculates the d-axis fundamental current reference signal and the q-axis fundamental current reference signal using a proportional-integral control principle.

9. The current conversion control device of the frequency converter according to claim 6, characterized in that: The final input signal of the current control module includes the difference between the sum of the d-axis fundamental current reference signal and the d-axis harmonic current signal and the d-axis compensation current component, and the difference between the sum of the q-axis fundamental current reference signal and the q-axis harmonic current signal and the q-axis compensation current component.

10. The current conversion control device of a frequency converter according to claim 6, characterized in that: Obtaining the d-axis harmonic current signal and the q-axis harmonic current signal that need to be compensated, specifically including: Perform Park transformation on the load current of the inverter to obtain the d-axis load current component and the q-axis load current component; Inputting the d-axis load current component and the q-axis load current component into a low-pass filter respectively to obtain a d-axis filtered current component and a q-axis filtered current component; The difference between the d-axis load current component and the d-axis filter current component is used as the d-axis harmonic current signal, and the difference between the q-axis load current component and the q-axis filter current component is used as the q-axis harmonic current signal.

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