A topology for reducing voltage ripple in uncontrolled rectification

Abstract

The application provides a topology for reducing uncontrolled rectification voltage ripple and a control method thereof, and belongs to the technical field of frequency converters, and comprises a three-phase full-bridge rectification module D, a direct-current reactance L, a direct-current current sensor CV2, a first capacitor filtering module C1, a load R, a capacitor voltage detection module TV1 and a three-phase power grid voltage detection module TV2; the application also provides a control method of the topology, reduces input side current harmonics when the frequency converter is in light load, reduces pollution to the power grid, reduces more than half of the capacitor capacity, and greatly reduces the size of the frequency converter.

Description

Technical Field

[0001] This invention belongs to the field of frequency converter technology, specifically relating to a topology for reducing uncontrolled rectified voltage ripple. Background Technology

[0002] Inverters are widely used in industrial control, with most being two-quadrant voltage source inverters using uncontrolled diodes for input rectification. However, this diode rectification method has significant drawbacks: large harmonic current components generated by the grid and voltage fluctuations at six times the frequency of the rectified voltage. Inverters often require a stable DC voltage to reduce output voltage harmonics and suppress torque fluctuations in the load motor. To achieve DC voltage stability, a filter consisting of a DC inductor and a DC filter capacitor is added to the inverter to filter out DC voltage fluctuations. However, DC inductors and DC filter capacitors are relatively large and expensive, especially in high-power inverters, where they account for a significant portion of the cost. Even with a four-quadrant inverter using PWM rectification, the size and cost of the three inductors on the input side, plus the full-power controlled rectifier switching device, cannot reach ideal levels. Summary of the Invention

[0003] In view of the above-mentioned shortcomings of the prior art, the present invention provides a topology for reducing uncontrolled rectified voltage ripple, so as to solve the above-mentioned technical problems.

[0004] The present invention provides a topology for reducing uncontrolled rectified voltage ripple, comprising: a three-phase full-bridge rectifier module D, a compensation module, a DC current sensor CV2, a first capacitor filter module C1, a load R, a capacitor voltage detection module TV1, and a three-phase grid voltage detection module TV2;

[0005] The three-phase grid voltage detection module TV2 and the three-phase full-bridge rectifier module D are connected to the grid. The compensation module is connected in series with the three-phase full-bridge rectifier module D. The first capacitor filter module C1 is connected to the compensation module. The load R is connected to the first capacitor filter module C1. The capacitor voltage detection module TV1 is connected in parallel across the first capacitor filter module C1. The compensation module includes a reactor branch and a controlled branch. The reactor branch includes a DC reactor L. A reactor L1 is set at the input end of the controlled branch. The controlled branch includes at least two H-bridge inverters INV connected in series. Each H-bridge inverter INV is connected to the second capacitor filter module C2. The second capacitor filter module C2 is connected to the single-phase full-bridge rectifier circuit. The single-phase full-bridge rectifier circuit is connected to the transformer T that supplies power. A first current sensor CV1 and a reactor L1 are set at the output end of the controlled branch.

[0006] The control method for the topology that reduces uncontrolled rectified voltage ripple includes:

[0007] The voltage signal at the capacitor terminal of the filter module is obtained through the voltage detection module TV1, and a stable DC voltage is obtained through signal processing.

[0008] The power grid detection module TV2 collects the three-phase power grid voltage signal and fits the power grid voltage signal to obtain the DC output voltage of the three-phase full-bridge rectifier module D;

[0009] The voltage feedforward command of the compensation module is calculated based on the stable DC voltage and the DC output voltage.

[0010] The total current signal on the bus is obtained by DC current sensor CV2, and a stable DC current is obtained by signal processing.

[0011] The current command of the compensation module is calculated based on the total current and the stable DC current.

[0012] The actual current of the compensation module is obtained through the first current sensor CV1;

[0013] The voltage command of the compensation module is determined based on the voltage feedforward command, current command, and actual current of the compensation module.

[0014] The drive signal for the H-bridge inverter INV is generated according to the voltage command of the compensation module using a carrier phase-shifting method.

[0015] Furthermore, the signal processing method is moving average filtering.

[0016] Furthermore, the voltage feedforward command of the compensation module is calculated based on the stable DC voltage and the DC output voltage; the formula is V. set =(V dc -V avr )×(l+l1) / l, where V set For voltage feedforward command, V avr To stabilize the DC voltage, V dc Let l be the DC output voltage, and l be the inductance value of the DC reactance L. l The inductance value of the reactor L1 is given.

[0017] Furthermore, the formula for calculating the current command of the compensation module based on the total current and the stable DC current is I. set =(I all -I avr ), where I set For current command, I all For the total current, I avr To stabilize the DC current.

[0018] Furthermore, the carrier phase shift angle is 180 degrees / N, where N is the number of INVs in the compensation inverter.

[0019] The beneficial effects of this invention are that it provides a topology for reducing uncontrolled rectifier voltage ripple. By adding a compensation module after the uncontrolled rectifier circuit, the input current harmonics under light load conditions can be significantly reduced, thus reducing pollution to the power grid. It can also reduce the capacitor capacity by more than half compared to conventional inverters, greatly reducing the size of the inverter and making the structure more compact, which is beneficial to improving the competitiveness of the product.

[0020] Furthermore, the design principle of this invention is reliable, the structure is simple, and it has a very wide range of application prospects. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the topology of one embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the structure of the compensation module in the topology of one embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram illustrating the calculation of relevant parameters for a control method provided in an embodiment of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0026] like Figure 1 As shown, this application provides a topology for reducing uncontrolled rectified voltage ripple, including: a three-phase full-bridge rectifier module D, a compensation module, a DC current sensor CV2, a first capacitor filter module C1, a load R, a capacitor voltage detection module TV1, and a three-phase grid voltage detection module TV2. In this topology, except for the compensation module, the remaining components constitute the main power circuit of the frequency converter;

[0027] In this configuration, the three-phase grid voltage detection module TV2 and the three-phase full-bridge rectifier module D are connected to the power grid. A compensation module is connected in series with the three-phase full-bridge rectifier module D. The first capacitor filter module C1 is connected to the compensation module. The load R is connected to the first capacitor filter module C1. The capacitor voltage detection module TV1 is connected in parallel across the first capacitor filter module C1. Figure 2 As shown, the compensation module includes: a reactor branch and a controlled branch; the reactor branch includes a DC reactor L; a reactor L1 is set at the input end of the controlled branch, and the controlled branch includes at least two H-bridge inverters INV connected in series; each H-bridge inverter INV is connected to a second capacitor filter module C2, the second capacitor filter module C2 is connected to a single-phase full-bridge rectifier circuit, the single-phase full-bridge rectifier circuit is connected to the corresponding power supply transformer T, and a first current sensor CV1 and a reactor L1 are set at the output end of the controlled branch.

[0028] This embodiment adds a compensation module to the DC circuit after uncontrolled rectification. The three-phase AC input power supply, after being rectified by uncontrolled devices, is connected in series with the compensation module, and then filtered by the first capacitor filter module C1 before supplying power to the inverter load. The compensation module consists of two branches: one is a reactor branch, and the other includes multiple controlled branches of H-bridge inverter INVs. The number of H-bridge inverter INVs is preset according to the grid voltage level. For example, the maximum output voltage of the compensation module needs to be approximately 12% of the bus voltage of the inverter's main power circuit. The maximum DC voltage of each H-bridge inverter INV is 1000V. In a 10kV inverter main power circuit, only two H-bridge inverter INVs connected in series are needed to meet the requirements. Therefore, the invention can be extended according to the voltage level of the inverter. Tests have proven that this topology is applicable to inverters with voltage levels from 0-10kV, and has a wide range of applications.

[0029] In this embodiment, the compensation module only compensates for the AC component of the current flowing through the DC reactance L. Therefore, the average power of the compensation module is zero, and the energy generated by the compensation module is only the heat loss of the device itself, which is very small. Using the topology provided in this application can effectively reduce harmonics on the input side of the frequency converter under light load, reduce harmonic interference to the power grid, and thus improve the performance of the frequency converter.

[0030] The output frequency of each H-bridge inverter INV in the controlled branch is 6 times the grid frequency. The average active power output during the fundamental cycle is basically 0. Therefore, the capacity of the single-phase full-bridge rectifier circuit of the compensation module and the second capacitor filter module C2 are very small. The power of the inverter section is only about 6% of the power of the H-bridge inverter INV, so the overall volume is not large.

[0031] In response to the above-mentioned topology, embodiments of this application also provide a control method for reducing uncontrolled rectified voltage ripple in the topology, including:

[0032] The voltage signal at the capacitor terminal of the first filter module C1 is obtained by the voltage detection module TV1, and the voltage signal is filtered by moving average to obtain a stable DC.

[0033] The three-phase grid voltage signal is acquired by the grid detection module TV2, and the DC output voltage of the three-phase full-bridge rectifier module D is obtained by fitting the grid voltage signal; specifically, the AC line voltage value V of the three-phase grid is acquired by the voltage detection module TV2. ab V bc V ca ; Calculate the absolute value of the voltage from the three voltage sources to obtain |V ab |、|V bc |、|V ca |;will|V ab |、|V bc |、|V ca The maximum value in | is used as the fitted DC output voltage of the three-phase full-bridge rectifier module D.

[0034] The voltage feedforward command of the compensation module is calculated based on the stable DC and DC output voltage, and the formula is V. set =(V dc -V avr )×(l+l1) / l, where V set For voltage feedforward command, V avr To stabilize the DC voltage, V dc Let l be the DC output voltage, and l be the inductance value of the DC reactance L. l The inductance value of the reactor L1 is given.

[0035] The total current signal I on the bus is obtained by the DC current sensor CV2. all The total current signal is then subjected to a moving average filter to obtain the stable DC current I. avr The current command of the compensation module is calculated based on the total current and the stable DC current value, using the formula I. set =(I all -I avr ), where I all For the total current, I avr To stabilize the DC current, I set This is a current command; the actual current I of the compensation module is obtained through the current sensor CV1. fdb .

[0036] According to the current closed-loop control method, based on the voltage feedforward command and current command I from the compensation module... set The voltage command of the compensation module is determined by the actual current; the voltage command of the compensation module consists of two parts, one part being the voltage feedforward command V.set The other part is the current command I. set With actual current I fdb The difference multiplied by the proportionality coefficient Kp, i.e. (I set -I fdb )*Kp.

[0037] like Figure 3 As shown, based on the voltage command of the redefined compensation module, N drive signals for the switching devices in the compensation inverter INV are generated using a carrier phase-shifting method, where the carrier phase-shifting angle is 180 degrees / N. Specifically, the voltage command of the compensation module is used as the modulation signal. The N compensation inverter INVs have N units. A triangular wave signal is obtained as the carrier wave of the first unit. Based on the number of units N, the triangular wave signal is sequentially shifted by 180 degrees / N, resulting in N triangular wave signals with different phases. The forward and reverse modulation signals are compared with the N triangular wave signals respectively to obtain the drive signals pwm1, pwm2, ..., pwmn for the switching devices in the N compensation inverter INVs.

[0038] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the invention by those skilled in the art without departing from the spirit and essence of the invention. Such modifications or substitutions should all fall within the scope of the invention, or any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the invention should be covered within the protection scope of the invention. Therefore, the protection scope of the invention should be determined by the scope of the claims.

Claims

1. A topology to reduce the voltage ripple of a non-controlled rectifier, characterized in that, The application relates to a topology for reducing uncontrolled rectification voltage ripples, which comprises the following components: a three-phase full-bridge rectification module D, a compensation module, a direct-current sensor CV2, a first capacitor filter module C1, a load R, a capacitor voltage detection module TV1 and a three-phase power grid voltage detection module TV2; wherein the three-phase power grid voltage detection module TV2 and the three-phase full-bridge rectification module D are connected to the power grid, the compensation module is connected in series with the three-phase full-bridge rectification module D, the first capacitor filter module C1 is connected with the compensation module, the load R is connected with the first capacitor filter module C1, and the capacitor voltage detection module TV1 is connected in parallel across the first capacitor filter module C1; the compensation module comprises an electric reactor branch and a controlled branch; the electric reactor branch comprises a direct-current reactor L; an electric reactor L1 is arranged at the input end of the controlled branch, the controlled branch comprises at least two H-bridge inverters INV connected in series, the output frequency of each H-bridge inverter INV in the controlled branch is 6 times the frequency of the power grid; each H-bridge inverter INV is connected with a second capacitor filter module C2, the second capacitor filter module C2 is connected with a single-phase full-bridge rectification loop, the single-phase full-bridge rectification loop is connected with a corresponding power supply transformer T, and a first current sensor CV1 and an electric reactor L1 are arranged at the output end of the controlled branch; the control method of the topology for reducing uncontrolled rectification voltage ripples comprises the following steps: acquiring a filter module capacitor end voltage signal through the voltage detection module TV1 and obtaining a stable direct-current voltage through signal processing; the power grid detection module TV2 collects a three-phase power grid voltage signal, and a direct-current output voltage of the three-phase full-bridge rectification module D is fitted through the three-phase power grid voltage signal; calculating a voltage feedforward instruction of the compensation module according to the stable direct-current voltage and the direct-current output voltage; acquiring a total current signal on the bus through the direct-current sensor CV2 and obtaining a stable direct-current current through signal processing; calculating a current instruction of the compensation module according to the total current and the stable direct-current current; acquiring an actual current of the compensation module through the first current sensor CV1; re-determining a voltage instruction of the compensation module according to the voltage feedforward instruction, the current instruction and the actual current of the compensation module; generating a drive signal of the H-bridge compensation inverter INV according to the re-determined voltage instruction of the compensation module through a carrier phase-shift method; The voltage feedforward instruction of the compensation module is calculated according to the stable direct current voltage and the direct current output voltage; the formula is V set =(V dc -V avr )×(l+l1) / l, wherein V set is the voltage instruction, V avr is the stable direct current voltage, V dc is the direct current output voltage, l is the inductance value of the direct current reactance L, and l l is the inductance value of the reactor L1; The formula for calculating the current instruction of the compensation module according to the total current and the stable direct current is I set = (I all -I avr ), wherein I set is the current instruction, I all is the total current, and I avr is the stable direct current.

2. The topology of claim 1, wherein, the signal processing mode is a sliding average filtering mode.

3. The topology of claim 1, wherein, The angle of the carrier phase-shift is 180 degrees / N, wherein N is the number of the compensation inverters INV.

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