JP2015136202A - chopper circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance efficiency of a step-up/down chopper circuit, paralleled by an interleave system, during low output.SOLUTION: Efficiency of a step-up/down chopper circuit, paralleled by an interleave system, during low output is enhanced by controlling the number of step-up/down chopper circuits to be operated by comparing the output current and a set threshold. Furthermore, the step-up/down chopper circuits are started and stopped while shifting the phase by (360°/the number of step-up/down chopper circuits started in parallel), depending on the number of step-up/down chopper circuits operated in parallel.

Description

  The present invention is used in a distributed power supply system in which a direct current power supply such as a solar battery or a fuel cell is connected to a system, etc. More particularly, the present invention relates to a circuit in which the step-up / step-down chopper circuit is multiplexed in parallel.

  In a distributed power supply system that supplies power to a load by connecting a solar battery or a fuel cell to a commercial power supply as a distributed power supply, a DC-DC converter that boosts the output voltage of the solar battery or the fuel cell because the power generation voltage is low. It is common to have. When a large current is supplied to a solar cell or a load, a plurality of unit chopper circuits are connected in parallel to share the output current. However, in the multiple parallel connection chopper circuit, the efficiency is not so bad when the output is large, but there is a problem that the efficiency is lowered at the time of low output.

JP 09-215322 A

  In Japanese Patent Laid-Open No. 09-215322, a current detector is provided for each chopper, a deviation between the output current and the average current is obtained, and a correction amount corresponding to the magnitude of the temporal variation of the current deviation is output. Further, the absolute value of the current deviation is calculated, it is determined whether or not the absolute value exceeds the reference voltage source, and the switch provided on the output side of the PID controller is turned on / off corresponding to the determination result, In a circuit in which a step-up / step-down chopper circuit that prevents unnecessary correction operation with a small current deviation is multiplexed in parallel, efficiency is improved at low output.

  In the circuit that performs feedback control described in Patent Document 1, it is possible to eliminate the imbalance of the output current and improve the efficiency at the time of low output, but the detector is required for the unit chopper, There exists a subject that a control part becomes complicated.

  An object of the present invention is to prevent the efficiency of a multiple parallel-connected chopper circuit from decreasing even at low output by simple control without complicating the control unit.

  In order to solve the above problems, the step-up / step-down chopper circuit according to the present invention measures the input / output current, confirms the load state, and controls the number of step-up / step-down chopper circuits to be operated according to the value. Control is performed so that the buck-boost chopper circuit is stopped at low output (light load) and the stopped buck-boost chopper circuit is started at medium-high output. Specifically, in a step-up / step-down chopper circuit connected in parallel to a common DC power supply, a means for measuring the output current is provided, and when the output current exceeds the n-unit operation upper limit threshold, the (n + 1) -th unit The step-up / step-down chopper circuit is soft-started with a specified current phase difference, and has means for stopping the n-th step-up / step-down chopper circuit when the output current falls below the n-unit operation lower limit threshold.

  In the step-up / step-down chopper circuits connected in parallel, the MAX efficiency point (current / voltage) of each step-up / step-down chopper circuit is measured in advance, and the number of step-up / step-down chopper circuits operated by the input / output current is controlled. Compare the input / output current and the threshold value to calculate the number of step-up / down choppers to be operated. Specifically, it is determined according to the flowchart of FIG. First, the MAX efficiency point (current / voltage) of one step-up / down chopper circuit is grasped (S20). The input current, input voltage, output current, and output voltage are measured (S21). Number of step-up / down chopper circuits = INT (measurement current / MAX efficiency point current) (S22). Next, the current phase after switching accompanying the turning on / off of the chopper circuit is calculated. Calculated current phase value after switching = 360 degrees / parallel number of step-up / down chopper circuits (S23).

  In the present invention, the threshold for switching the number of operating units is set with reference to the maximum output of one device so that the number of operating units does not frequently switch. FIG. 3 shows an example of the setting. When mode 1 or 1 unit operation is performed, for example, when 90A is set to the second switch setting value, 90A is slightly exceeded, and after switching to mode 2 unit operation, 90A is immediately divided. The mode is switched to mode 1. If frequent switching occurs, switching loss will occur many times. In order to prevent frequent switching, the switching lower limit threshold is set to 85A, for example, so that frequent switching does not occur. In addition, a soft start is performed to start and stop the buck-boost chopper and to switch the number of operating units.

  According to the present invention, it is possible to perform a stable and highly efficient operation from a low output to a rated output without changing the circuit configuration.

Circuit configuration example in the present invention (3-parallel step-down chopper circuit) Operation flowchart of the present invention Number determination flowchart of the present invention Chopper input unit control setting example (3 units) Movement of controlling the number of chopper inputs Efficiency calculation simulation of chopper circuit Power factor comparison between conventional circuit and the present invention

  The present invention will be described with reference to FIGS. FIG. 1 shows a 30 kW system composed of three parallel step-down chopper circuits, each of which has a 10 kW circuit (rated input voltage 200 V, rated output current 100 A, output voltage 100 V) connected in parallel. FIG. 6 shows a simulation result of a general switching device IGBT with this circuit configuration.

The operation of the present invention in a three parallel step-down chopper circuit will be described with reference to FIGS. FIG. 4 shows a setting example of the input number. Mode 1, 1 unit start (Unit 1 start). Mode 2 and 2 units start (Unit 1 and Unit 2 start), Mode 3 and 3 units start (Unit 1, Unit 2, Unit 3 all start). The value of the output current when the output current rises from the mode 1 state and shifts to the mode 2 is defined as one unit upper limit threshold value. In this embodiment, it is 90A. When the above-mentioned one-unit upper limit threshold is exceeded, the mode is shifted to two-unit operation. The value of the output current when shifting to mode 3 during the operation of two units in mode 2 is defined as the upper limit threshold value for two units. In this embodiment, it is 180A. Similarly, the value of the output current when shifting from mode 3 to mode 2 is defined as the lower limit threshold of three units, and the value of the output current value when shifting from mode 2 to mode 1 is defined as the lower limit threshold of two units. Define.
In this embodiment, the lower limit threshold value for the three units is set to 170A, and the lower limit threshold value for the two units is set to 85A.

  The operation of this embodiment will be described with reference to the operation flowchart of FIG. 3 and FIGS. <Mode 1> First, the first unit is activated (S1). The output current is constantly measured, and when the output current becomes equal to or higher than the single-unit operation upper limit setting threshold 90A, the mode is shifted to mode 2 (S2). Unit 2 is on standby, and when the current phase of Unit 1 is delayed by 180 °, Unit 2 is soft-started and activated (S3). When the output current amount is equal to or greater than the two-unit operation upper limit setting threshold value 180A, the mode shifts to mode 3 (S5). At the same time that the current phase delay of Unit 2 gradually advances from 180 ° to 120 °, and at the time of 240 ° delay from the Unit 1 current phase, Unit 3 is soft-started and started (S6).

  In the three-unit parallel step-down chopper circuit, at the time of high output, the three-unit parallel operation is continued as it is (the mode 3 state is maintained). When the output current amount falls below the three-unit operation lower limit setting threshold 170A (S7), the third unit is soft-started and stopped (S8). The mode is changed and the current phase delay of Unit 2 is gradually advanced from 120 ° to 180 °. When the output current amount falls below the two-unit operation lower limit setting threshold 85A (S4), the second unit is soft-started and stopped, and the mode 1 is entered (S9).

  FIG. 7 shows a comparison in efficiency between the conventional example and the number control of the present invention. Even in the conventional method, the efficiency is maintained as high as 98.4% near the output rating. However, the efficiency decreases as the output decreases. When the output current is 60 A, the efficiency is 97. It has dropped to 6%. By controlling the number of operating units according to the output current as in the embodiment of the present invention, the load factor is 20% to 100%, and the efficiency can be maintained at the high efficiency of 98.4% at the rated time. Efficiency can be increased.

  In the present embodiment, three parallel step-down chopper circuits are used, but the same control is also performed in the step-up chopper circuit, so that the efficiency at low load can be increased. When the number of units in parallel is four or more, adaptation is possible by performing the same control.

1 DC power supply 2 C1 (capacitor)
3 SW1
4 SW2
5 SW3
6 D1 (diode)
7 D2 (diode)
8 D3 (diode)
9 L1 (reactor)
10 L2 (reactor)
11 L3 (reactor)
12 C2 (capacitor)
13 Load 14 Total input current 15 Total output current 16 Load current

Claims (3)

In a buck-boost chopper circuit connected in parallel to a common DC power supply, the means to measure the output current and the (n + 1) th buck-boost chopper circuit are specified when the output current exceeds the upper limit threshold of n units Starts with a soft start with a current phase difference of, and when the output current falls below the n-unit operation lower threshold, the nth step-up / down chopper circuit is stopped with a soft-start with a specified current phase difference Step-up / down chopper circuit characterized by comprising In the step-up / step-down chopper circuits connected in parallel, the MAX efficiency point (current / voltage) of each step-up / step-down chopper circuit is measured in advance, and n units for determining the number of step-up / step-down chopper circuits to be operated by input / output current are determined. 2. The step-up / step-down chopper circuit according to claim 1, further comprising means for setting an operation upper limit threshold value and an n-unit operation lower limit threshold value. The specified current phase difference after changing the number of units according to the start / stop of the step-up / step-down chopper circuit is (360 ° / number of parallel start-up / step-down chopper circuits). The described buck-boost chopper circuit

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