Background
The variable frequency speed control technology has become an important means for saving energy, reducing consumption, improving process flow, improving product quality and environment and promoting technical progress in the industrial field, and various high-power frequency converters are widely applied to large-scale industrial production equipment along with the development of novel high-power electronic devices. At present, an active front-end AC-DC-AC topology is adopted as a mainstream structure of a high-performance high-power frequency converter.
The rated capacity test is one of the most important test contents of the frequency converter, and for medium and small power frequency converters, the traditional rated capacity test methods mainly comprise two methods: one is the tested frequency converter output load with passive impedance, and the other is the tested frequency converter output load with active load of the frequency converter-motor unit.
When the tested frequency converter outputs an active load with a frequency converter-motor unit, two motors with the power equivalent to that of the tested frequency converter are coaxially or connected through a gear box to form the unit, one motor is controlled by a set of accompanying converter, and the other motor is controlled by the tested frequency converter. In the test, the test-accompanying converter and the tested frequency converter are controlled to enable one motor to run in an electric state and the other motor to run in a power generation state, so that a required rated test torque is formed between the two motors in the set, back-to-back type power flow is formed, and the loss of the set and the loss of the test-accompanying converter are greatly reduced compared with the loss of passive impedance in a passive impedance load of an output belt of the tested frequency converter. During testing, the converter to be tested generally works in a torque closed loop, the frequency converter to be tested works in a speed closed loop, a frequency closed loop or an open loop, the converter to be tested controls the torque direction, the frequency converter to be tested controls the speed direction, and the four-quadrant reversible operation test is realized through the combination of the speed polarity and the torque polarity. The test method has the advantages that reversible tests can be carried out, steady-state and dynamic performance tests can be carried out, the power loss in the test process is small, and the like; the defects are that the unit equipment and the accompanying converter system are complex, the equipment investment is large, the occupied area of a laboratory is large, the mechanical equipment is difficult to maintain, and the accompanying converter system is not suitable for the rated capacity test of a high-power or ultra-high-power tested frequency converter.
For a high-power or ultra-high-power frequency converter, because of the limitation of the capacity of test equipment (such as a frequency converter-motor unit), a field, the power supply capacity and the like, a stable rated capacity test is difficult to perform, a rated temperature rise and loss test and a test can be generally performed according to units, then the whole rated capacity of the frequency converter is estimated, or an actual test is performed on the operation site of the frequency converter, but the site test generally has difficult continuous and stable rated operation working conditions. Most of the reported test methods are directed at power devices or power units, and few test methods are directed at the whole rated capacity of the high-power frequency converter. Therefore, it is necessary to research a rated capacity testing method for efficient energy saving of the ac-dc-ac frequency converter.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a rated capacity test method for an active front-end voltage type AC-DC-AC frequency converter, which comprises reversible operation, steady-state operation tests of rated capacity under different load power factors and the like, and can accurately test the rated output of the whole frequency converter and the temperature rise of a power device.
The technical problem to be solved by the invention is realized by adopting the following technical scheme:
a rated capacity test method of an active front-end voltage type AC-DC-AC frequency converter comprises the following steps:
(1) an active front end rectifier AFER and an inverter INV of a frequency converter are respectively connected to a power grid through a transformer device to form a closed loop test loop;
(2) establishing a test control system by adopting an active power and reactive power independent vector control mode;
(3) by adjusting the related setting of the AFER and the INV, the power and the output power factor of the frequency converter can be flexibly adjusted, reversible operation tests of rated capacity under different power factors are carried out, and the rated capacity of the whole frequency converter and the temperature rise of a power device are tested.
Moreover, the method for connecting the active front end rectifier AFER and the inverter INV of the frequency converter into the power grid through the transformer device comprises the following steps: the active front end rectifier AFER and the inverter INV of the frequency converter are respectively connected into a power grid through a transformer T1 and a transformer T2, or the active front end rectifier AFER and the inverter INV of the frequency converter are respectively connected into the power grid through two splitting transformers T, or the active front end rectifier AFER and the inverter INV of the frequency converter are respectively connected into the power grid through a transformer T1 and a reactor TD.
Furthermore, said associated settings include a reactive current setting of AFER, an active current setting and a reactive current setting of inverter INV.
Moreover, the method for adjusting the power and the output power factor of the frequency converter comprises the following steps: active power and reactive power according to test requirementsCalculating the active current under various operating conditions by power
And reactive current
After the power is switched on, order
When in use
When in use, active power and reactive power flow from the power grid in the forward direction through a closed loop T1 → AFER → INV → T2 → T1; when in use
When active power flows in a forward direction from the power grid through the closed loop T1 → AFER → INV → T2 → T1, and reactive power flows in a reverse direction from the power grid through the closed loop T1 → AFER → INV → T2 → T1; when in use
When in use, active power and reactive power reversely flow from the power grid through a closed loop T1 → AFER → INV → T2 → T1; when in use
In time, active power flows in reverse direction from the power grid through the closed loop T1 → AFER → INV → T2 → T1, and reactive power flows in forward direction from the power grid through the closed loop T1 → AFER → INV → T2 → T1.
And the active front end voltage type AC-DC-AC frequency converter mainly comprises an active front end rectifier AFER, an inverter INV and a DC filter capacitor.
And the active front end rectifier AFER and the inverter INV are of two circuit structures with the same topology, and the direct current side is connected back to back through a filter capacitor to form an active front end voltage type AC-DC-AC frequency converter.
The invention has the advantages and positive effects that:
1. the test method has simple circuit and less equipment. Except the tested frequency converter, only two transformers (or one transformer and two cracking transformers, or one transformer and one reactor) and circuit switches are needed. Compared with an active load test method of the frequency converter-motor unit, the problems of installation, corollary equipment and mechanical maintenance of the frequency converter-motor unit are not required to be solved.
2. Compared with an active load test method of a frequency converter-motor unit, the test method has the advantages of no motor loss, unit mechanical loss, unit cooling loss and the like, low power consumption and high efficiency.
3. The test method can be used for testing different powers and different power factors required by the frequency converter, simulating the operation conditions under various power factor conditions, and realizing the reversible operation test.
4. The test method can test the temperature rise and the loss of each power device of the frequency converter under different power factors, thereby accurately evaluating the rated output capacity of the frequency converter under different power factors.
Detailed Description
The embodiments of the invention will be described in further detail below with reference to the accompanying drawings:
a test method of an active front-end voltage type AC-DC-AC frequency converter is disclosed.
A rated capacity test method for an active front-end voltage type AC-DC-AC frequency converter is used for comprehensively testing the performance of the active front-end voltage type AC-DC-AC frequency converter and comprises the following steps:
step 1: and respectively connecting an active front end rectifier AFER and an inverter INV of the frequency converter into a power grid through a transformer device to form a closed loop test loop.
Connecting the active front end rectifier AFER and the inverter INV of the active front end voltage type ac-dc-ac frequency converter to the power grid through transformers T1, T2 and switches S1, S2 as shown in fig. 1, or connecting the active front end rectifier AFER and the inverter INV of the active front end voltage type ac-dc-ac frequency converter to the power grid through two split transformers T and switches S as shown in fig. 2; alternatively, as shown in fig. 3, the active front end rectifier AFER and the inverter INV of the active front end voltage type ac-dc-ac frequency converter are connected to the power grid through the transformer T1, the reactor TD and the switches S1, S2. The active front end voltage type AC-DC-AC frequency converter mainly comprises an active front end rectifier AFER, an inverter INV and a DC filter capacitor. The test loop enables the energy of the power grid to be input into the frequency converter from the active front end rectifier AFER and to be fed back to the power grid from the frequency converter through the inverter INV to form a loop of power flow; meanwhile, the leakage reactance of the transformer can also be used as the load reactance of the AFER. Taking the configuration shown in fig. 1 as an example, AFER and INV are connected to the power grid through transformers T1 and T2, respectively. In the test, the power forms a closed loop through T1 → AFER → INV → T2 → T1, and for the convenience of the following description, it is specified that the power flowing from the grid side into AFER or INV is positive, whereas the power flowing from AFER or INV into the power grid is negative. The power flow polarities specified here are in fact the polarities of the active and reactive currents, since they are oriented in the power grid voltage vector.
Step 2: the control software of the inverter is modified according to the control block diagram shown in fig. 4, or the same controller as the rectifier is adopted for the inverter. The control system of the inverter in most frequency converters is designed for the frequency conversion and speed regulation of the motor, and when the test method is adopted, the control system is required to adopt the independent vector control of the active power and the reactive power, so that the control system of the inverter needs to be modified properly.
And step 3: by adjusting the related setting of the AFER and the INV, the power and the output power factor of the frequency converter can be flexibly adjusted, reversible operation tests of rated capacity under different power factors are carried out, and the rated capacity of the whole frequency converter and the temperature rise of a power device are tested.
As shown in fig. 4, the AFER operates as follows: the phase theta and the amplitude U of the voltage vector of the power grid are detected by taking the three-phase voltage signal of the power grid to a phase-locked loop PLL
d(ii) a Setting a DC voltage rating
With the actual value U of the DC voltage
dcAfter comparison, the direct current voltage is subjected to closed-loop regulation control through a voltage regulator AUR, and the output of the voltage regulator AUR is used as active current to be given
Reactive current setting
Calculating according to a power factor preset by experiments; detecting AFER three-phase alternating currentThe actual value i of the active current is calculated by 3/2 transformation and vector revolution VD1 of the current signal
iPAnd the actual value of the reactive current i
iQ(ii) a Active current setting
With the actual value of the active current i
iPReactive current setting
With the actual value of the reactive current i
iQAfter the comparison, the closed-loop regulation is carried out through the current regulators ACR1 and ACR2 respectively, and the voltage is output as an active vector axis voltage additional given value and a reactive vector axis voltage given value; voltage feedforward signal U of active vector axis voltage additional given and PLL output
dSuperposing the voltage as an active vector axis voltage setting; the active vector axis voltage setting and the reactive vector axis voltage setting are converted through vector revolution VD2 and 2/3 to obtain a three-phase alternating voltage setting; and controlling a power switch device in the AFER to work through a Pulse Width Modulation (PWM) control link and a pulse isolation amplification link.
As shown in fig. 4, the INV operation principle is as follows: calculating and setting active current set according to test requirements
And reactive current setting
Detecting INV three-phase AC current signal, calculating active current actual value i by 3/2 transformation and vector revolution VD3
oPAnd the actual value of the reactive current i
oQ(ii) a Active current setting
With the actual value of the active current i
oPReactive current setting
With the actual value of the reactive current i
oQAfter the comparison, the respective current regulators ACR3 and ACR4 are closedLoop regulation, namely outputting the additional given active vector axis voltage and the given reactive vector axis voltage; voltage feedforward signal U of active vector axis voltage additional given and PLL output
dSuperposing the voltage as an active vector axis voltage setting; the active vector axis voltage setting and the reactive vector axis voltage setting are converted through vector revolution VD4 and 2/3 to obtain an INV three-phase alternating voltage setting; and controlling a power switch device in the INV to work through a Pulse Width Modulation (PWM) control and pulse isolation amplification link.
In the frequency converter topology, AFER adopts double closed-loop control of a direct-current voltage outer loop and a current inner loop, and INV adopts current closed-loop control, so that static-error-free control of direct-current bus voltage and static-error-free control of active power and reactive power can be realized. When INV active current is given
(or reactive current given
) Setting according to test requirements, changing direct current voltage in dynamic state, keeping the direct current bus voltage stable through double closed loop regulation control of an AFER direct current voltage outer loop and a current inner loop, and enabling an active current i flowing through the AFER in steady state
iP(or reactive current i
iQ) And INV active current i
oP(or reactive current i
oQ) Equal and opposite, the closed loop through T1 → AFER → INV → T2 → T1 forms the active (or reactive) power flow.
In this step, the relevant settings include a reactive current setting of AFER, an active current setting and a reactive current setting of inverter INV; the method for flexibly adjusting the power and the output power factor of the frequency converter comprises the following steps: calculating the active current under various operating conditions according to the active power and the reactive power required by the test
And reactive current
When the power supply is switched on, order
When in use
When in use, active power and reactive power flow from the power grid in the forward direction through a closed loop T1 → AFER → INV → T2 → T1; when in use
When active power flows in a forward direction from the power grid through the closed loop T1 → AFER → INV → T2 → T1, and reactive power flows in a reverse direction from the power grid through the closed loop T1 → AFER → INV → T2 → T1; when in use
When in use, active power and reactive power reversely flow from the power grid through a closed loop T1 → AFER → INV → T2 → T1; when in use
In time, active power flows in reverse direction from the power grid through the closed loop T1 → AFER → INV → T2 → T1, and reactive power flows in forward direction from the power grid through the closed loop T1 → AFER → INV → T2 → T1. Therefore, the method can realize the reversible operation test of the active front-end voltage type AC-DC-AC frequency converter.
During the test, the active current was varied as required
And reactive current
And setting, measuring the temperature rise of each power device under each working condition, and determining the rated power of the frequency converter allowed under different power factors according to the measurement result and the allowed temperature rise of each power device.
The temperature rise of the power device is closely related to the operation condition and the power factor of the frequency converterThe test method can flexibly adjust the power and the power factor according to the test requirement, and accurately simulate and test the temperature rise of the power device under different power factors and under rated working conditions. In order to illustrate the influence of the power factor of the frequency converter on the temperature rise of the power devices, a current flowing path and the loss condition of each power device when the frequency converter works are analyzed by taking a diode-clamped three-level inverter as an example. Fig. 5 shows the variation of the one-phase voltage fundamental wave u output by the inverter and the variation of the one-phase voltage fundamental wave i in one cycle,
![Figure BDA00001051804400000610](https://patentimages.storage.***apis.com/11/09/8a/faa3a292958652/BDA00001051804400000610.png)
is the power factor angle. According to the situation of the zero crossing point of the voltage and the current in the figure, the whole period can be divided into four intervals for analysis respectively:
The current path is shown in fig. 6 a). This interval u is positive and i is negative. Due to the pulse width modulation the actual ac side voltage is switched between positive and zero. V1 and V3 are alternately conducted, and V2 is always in a conducting state. When the voltage on the alternating current side is in a positive state, current flows into the direct current positive bus through the D1 and the D2; in the ac side voltage zero state, current flows into the zero dc bus via V3 and D6. In the process, almost no current flows in the V1, and the loss is small; v3 has both conduction and switching losses; the freewheeling diodes D1 and D2 flow current when they are turned on, and there is conduction loss; d1 experiences back pressure at turn-off and there is a reverse recovery loss, while D2 experiences no back pressure and no reverse recovery loss at turn-off due to V2 and V3 being on.
The current path is shown in fig. 6 b). The interval u is positive and i is positive. Due to the pulse width modulation the actual ac side voltage is switched between positive and zero. V1 and V3 are alternately conducted, and V2 is always in a conducting state. When the voltage on the alternating current side is in a positive state, current flows out through V1 and V2; in the ac side voltage zero state, current flows through V2 and D5. Similar to the analysis of interval 1), when V1 has both conduction loss and switching loss, V2 has conduction loss; d5 is subject to back pressure when turned off and there are reverse recovery losses.
The current path is shown in fig. 6 c). This interval u is negative and i is positive. Due to the pulse width modulation the actual ac side voltage is switched between negative and zero. V2 and V4 are turned on alternately, and V3 is always in a conducting state. When the voltage on the alternating current side is in a negative state, current flows out through D3 and D4; in the ac side voltage zero state, current flows through V2 and D5. In this interval, the V2 tube has conduction loss and switching loss; the D3 tube has conduction loss; the D4 tube has both conduction and reverse recovery losses.
The current path is shown in fig. 6 d). This interval u is negative and i is negative. Due to the pulse width modulation the actual ac side voltage is switched between negative and zero. V2 and V4 are turned on alternately, and V3 is always in a conducting state. When the voltage on the alternating current side is in a negative state, current flows into the direct current negative bus through V3 and V4; in the ac side voltage zero state, a current flows through V3 and D6. In this interval, V3 and V4 flow current when they are on, and there is conduction loss; v4 also has switching losses due to switching action; d6 has reverse recovery loss.
The analysis shows that when the voltage type AC-DC-AC frequency converter works, the magnitude and the time of current flowing in the power device are related to the power factor and the voltage amplitude of the AC side, so the temperature rise of the device is also related to the power factor. Therefore, by adopting the test method, the loss and the temperature rise of the frequency converter under various working conditions can be comprehensively tested by adjusting the power factor output by the inverter, and the rated output capacity of the device under different power factors can be accurately evaluated.
It should be emphasized that the embodiments described herein are illustrative rather than restrictive, and thus the present invention is not limited to the embodiments described in the detailed description, but other embodiments derived from the technical solutions of the present invention by those skilled in the art are also within the scope of the present invention.