Power conversion device

Patent metadata

Field	Value
Publication number	US-9735619-B2
Application number	US-201214370164-A
Country	US
Kind code	B2
Filing date	Aug 21, 2012
Priority date	Feb 8, 2012
Publication date	Aug 15, 2017
Grant date	Aug 15, 2017

Abstract

A power conversion device connected between a storage battery and AC system charges the storage battery with power from the AC system and discharges power from the storage battery to the AC system. The power conversion device includes a DC/DC conversion circuit performing conversion between a storage battery voltage and DC bus voltage, a DC/AC conversion circuit performing conversion between the DC bus voltage and AC voltage of the AC system, and control circuits controlling the DC/DC and DC/AC conversion circuits. The control circuits select either step-up control or step-down control for the DC/DC conversion circuit based on the storage battery voltage, the storage battery charge state, and a control range of the DC bus voltage, set a control target value of the DC bus voltage, and control the DC/DC and DC/AC conversion circuits by the selected control method so the DC bus voltage becomes the control target value.

First claim

The invention claimed is:

1. A power conversion device, connected between a storage battery and an AC system, which charges the storage battery with power from the AC system and discharges power from the storage battery to the AC system, the power conversion device comprising:
a DC/DC conversion circuit for performing conversion between a storage battery voltage of the storage battery and a DC bus voltage;
a DC/AC conversion circuit for performing conversion between the DC bus voltage and an AC voltage of the AC system; and
control circuits for controlling the DC/DC conversion circuit and the DC/AC conversion circuit, wherein
the control circuits
select one of four available controls as a selected control method for the DC/DC conversion circuit based on the storage battery voltage, a state of charge of the storage battery, and a control range of the DC bus voltage,
the four available controls including a first step-up control in a case of charging the storage battery with power from the AC system, a first step-down control in the case of charging the storage battery with power from the AC system, a second step-up control in a case of discharging power from the storage battery to the AC system, and a second step-down control in the case of discharging power from the storage battery to the AC system,

set a control target value of the DC bus voltage, and
control the DC/DC conversion circuit and the DC/AC conversion circuit by the selected control method so that the DC bus voltage becomes the control target value.

2. The power conversion device according to claim 1 , wherein, in the case of charging the storage battery with power from the AC system,
the control circuits
select, as the selected control method, the first step-down control method when the state of charge is smaller than a first predetermined value or is equal to or greater than a second predetermined value, or the first step-up control method when the state of charge is equal to or greater than the first predetermined value and is smaller than the second predetermined value, and
keep each selected control method when a control target value of the DC bus voltage set based on the selected control method falls within the control range of the DC bus voltage, or select one of the first step-down control and the first step-up control, that is different from each selected control method, when the control target value does not fall within the control range of the DC bus voltage.

3. The power conversion device according to claim 1 , wherein, in the case of charging the storage battery with power from the AC system,
the control circuits receive a step-down maximum charge current value that is a maximum charge current value allowed in the step-down control method, and a temperature of the storage battery, and compares the step-down maximum charge current value with a maximum charge current value that can be flowed into the storage battery at the temperature,
if the step-down maximum charge current value is smaller than the maximum charge current value, the control circuits
select, as the selected control method, the first step-down control method when the state of charge is smaller than a first predetermined value or is equal to or greater than a second predetermined value, or the first step-up control method when the state of charge is equal to or greater than the first predetermined value and is smaller than the second predetermined value, and
keep each selected control method when a control target value of the DC bus voltage set based on the selected control method falls within the control range of the DC bus voltage, or selects one of the first step-down control and the first step-up control, that is different from each selected control method, when the control target value does not fall within the control range of the DC bus voltage, and

if the step-down maximum charge current value is equal to or greater than the maximum charge current value, the control circuits always select the first step-down control method.

4. The power conversion device according to claim 1 , wherein, in the case of discharging power from the storage battery to the AC system,
the control circuits
select, as the selected control method, the second step-down control method when the state of charge is smaller than a fourth predetermined value, or the second step-up control method when the state of charge is equal to or greater than the fourth predetermined value, and
keep each selected control method when a control target value of the DC bus voltage set based on the selected control method falls within the control range of the DC bus voltage, or select one of the second step-down control and the second step-up control, that is different from each selected control method, when the control target value does not fall within the control range of the DC bus voltage.

5. The power conversion device according to claim 1 , wherein an AC power supply and an AC load are connected to the AC system, and in the case of discharging power from the storage battery to the AC system, a response speed of a control system is changed in accordance with whether the AC power supply is in a normal state or a power outage state, so that operation of the control system relevant to discharge control for the storage battery when the AC power supply is in a power outage state becomes faster than when the AC power supply is in a normal state.

6. The power conversion device according to claim 1 , wherein the control circuits
receive a current target instruction value for predetermined charging or discharging, and a temperature of the storage battery, and compare the current target instruction value with a current maximum value for the charging or discharging, that can be flowed into the storage battery at the temperature,
if the current target instruction value is equal to or greater than the current maximum value, set the current maximum value as a current control target value for the charging or discharging, and
if the current target instruction value is smaller than the current maximum value, set the current target instruction value as the current control target value.

7. The power conversion device according to claim 6 , wherein the control circuits control the DC/DC conversion circuit and the DC/AC conversion circuit so that current of the storage battery increases from an initial value thereof to the current control target value at a rate of predetermined time constant.

8. The power conversion device according to claim 1 , wherein when switching of a control method for the DC/DC conversion circuit from step-up control to step-down control or from step-down control to step-up control, the control method before the switching is stopped once, current of the storage battery is made to be zero, and the control method after the switching is started after a control variable of the control method is initialized once.

9. The power conversion device according to claim 1 , wherein
the DC/DC conversion circuit is composed of a DC/AC converter having switching devices, for performing conversion between the storage battery voltage and intermediate AC voltage, and an AC/DC converter having switching devices, for performing conversion between the intermediate AC voltage and the DC bus voltage,
when the DC/DC conversion circuit performs the first step-down control, switching operation of the switching devices of the DC/AC converter, and
when the DC/DC conversion circuit performs the second step-down control, switching operation of the switching devices of the AC/DC converter is stopped.

Assignees

• Inoue Sadayuki
• Mitsubishi Electric Corp

Inventors

• Inoue Sadayuki

Classifications

• H02J7/63

  against overdischarge · CPC title

• H02J7/62

  against overcurrent · CPC title

• H02J7/61

  against overcharge · CPC title

• H02J7/977 Primary

  of the battery · CPC title

• H02M3/33584

  Bidirectional converters · CPC title